DVD type magazines, races on speed, countless hours reading tuner mags, boards like HAN for example, reading owners manuals, repair manuals, hangin around shops and salvage yards... just to name a few that I can think of right now... point being I picked up the most knowledge while in situations I was into and havin fun with, as opposed to trying to cram from a book.
And I don't even compare to some of these guys. I definetely don't consider myself a mechanic and wont even attempt some jobs without a pros help.
I think I pick up something new everytime I get psyched about being around cars and car lovers. Which is where I think you want to be mentally to learn and retain stuff.