Without getting too philosophical I would like to lay out a couple of conclusions I have reached about learning in my experience so far.

I am an avid reader of technical and business literature and I enjoy it because it answers questions I may or may not have needed to face yet. For me learning is a way to improve judgement and decision making, preferably before those decisions are needed - especially when it comes to Business or Technical architecture.
Here is what I have found out about learning:

1. Your creativity is directly proportional to the diversity of your knowledge. - Here creativity stands for innovative thinking in any discipline. Creativity in any shape and form appears to be a result of the brain’s ability to cross-connect knowledge between subjects it knows. “Ray Bradbury describes it as stuffing your brain with seeds of all kinds, when you least expect, those seeds will sprout into something you never could have imagined.” /Keith Reinhard/ Leonardo Da Vinci’s Mona Lisa would not look the same without his knowledge of Math and Physics, just like his technical inventions would have not been the same without his artistic skills.  That is why I believe that if your future depends on innovative thinking or vision, you will benefit from expanding your knowledge into areas that would diversify your perspective.
2. Your brain is strongest in the areas you use it the most. - The mind is flexible and just like a muscle, it constantly shifts and grows in the areas it is being utilized the most, at the expense of unused areas. There are benefits and drawbacks to that. The drawback is that you may have forever lost a lot of the knowledge you’ve worked so hard to gain in High-School. The benefit is that your brain can catch up with whatever your next challenge is, if you hammer enough of your required new knowledge in it with discipline. In other words, you can certainly switch to Brain Surgery even if you are already a certified Rocket Scientist just as fast as a college grad would (I actually know someone who has done that already). In fact, you can switch to anything with enough discipline (in this case discipline, not brain capabilities are the hard part).
3. Your brain is faster than your mind. - During situations usually considered “important”, “fast”, or “urgent” your brain will weigh in what it knows unconsciously through practice far more than what your conscious mind can process and deliver. Scientists label this Autonomic versus Reactionary thinking, where your auto-responses weigh in the subconscious response, while your reactionary brain decides with your slower, conscious mind what to do in slightly more complicated and less automated situations. To illustrate this principle, calculate and compare the time it takes to complete these two scenarios:
   • Your reaction to an object that appears in front of you on a highway while you are moving at 60 mph.
   • Your description of a reaction you should make in response an object that appears in front of you on a highway while you are moving at 60 mph.

The reason I am separating Brain from Mind in statement #3 is because we, humans,  know so little about our own body and brain that we have studies ranging from Neurology to Psychology, Behavioral and Social Sciences, that try to “explain” in human terms what our own body does naturally. In fact, a great book called “On Intelligence” mentions that at this point of science, today, Neurology takes 9 years to study because it is still a science describing a minutiae of tiny details, and not a big picture suitable for deductive reasoning. We have yet to discover the links that would give us a bigger picture in less words.
That is why, when it comes to studies there is benefit to trying to comprehend how we learn naturally, as it would allow us to follow a pattern that is the path of least resistance for our own brain. Whether you choose books, lectures, audio or video learning study what your mind absorbs best, not what is cheapest or most available.
Here are couple of quotients I use for evaluating learning:
Amount of information absorbed / dollar spent - should drive your choice of media.
Amount of valuable information absorbed / total information received- is the signal to noise ratio that should drive your selection of authors within the media you choose.
A great quote from Guy Kawasaki’s Reality Check describes the best form of learning:
“A truly good book teaches me better than to read it. I must soon lay it down and commence living on its hint. What I begin by reading, I must finish by acting.“ - Henry David Thoreau
In short, surround thyself with good sources of knowledge. What you gain with learning is something nobody can take away. At the same time, your brain and the training you provide to your conscious and unconscious mind, will be the engine that drives your body, decisions, family, faith, career, and life.

Now back to some tools for perpetual learning. Here is the list of things I do to stay sharp, following the above presumptions:

1. I have given in and bought a Kindle… and it has paid for itself in several ways. The books I am now buying are much cheaper through the Kindle digital content store. 2. The Kindle’s ability to “suck-you-into-reading” has resulted in me reading every book I buy much faster because I am able to listen to my books with the surprisingly effective text-to-speech feature while driving, or doing chores. 3. My Knowledge-Gained-per-Dollar-Spent index and Percent-of-books-bought-that-are-actually-read indexes have gotten much better as a result. I am currently able to cover about 4000 units of Kindle content (not pages) per week.
2. I have also began following several phenomenal sources of free first-class knowledge listed here:
   • MIT’s Open Courseware
   • Academic Earth
   • Stanford on ITunes U (I highly recommend the Evidence-Based Management Lecture)
   • TED.com
   • The local Library or Bookstore
3. I have actively sought out business and technical literature titles present in recognized curriculums of Masters Programs such as Top MBA and MS in Computer Science programs (Harvard, Stanford, Wharton, MIT, Kellogg, Chicago GSB, Georgia Institute of Technology etc)
4. The information I am reading/watching is selected based on skills I want to develop, in different areas rather than a specialty, author, or subject. So far I have worked on and continue to seek solid grounding in Negotiations, Management, Strategy, Product Development & Marketing, Cross-Language Programming Best Practices, Design Patterns, JavaScript, ActionScript 3, Ajax, Perl, Python, Ruby on Rails, IPhone App development, PHP etc…

The goal is to anticipate and prepare with skills you expect to need in the near and distant future, rather than try to catch up with projects as they come.

The benefit, at least for me, has been in the comfort of knowing that at the time I need an ability, I have already read and internalized the essentials, limitations, and the available toolset in that area. With negotiations, for example, learning done on the side in College, for me, lead to a higher starting salary, a lower starting rent, a significantly lower first-new-car price, and more effective creative mutually beneficial solutions to professional and personal negotiations on a daily basis years after graduation. Needless to say you can stay sharp in many ways.

The important thing to internalize is the approach to learning that fits your natural mindset and the discipline to continue learning in order to remain relevant and avoid boredom.