Let's take a hypothetical case of a businessman who wanted to learn more about poker. Funding a session of poker is no problem but he wants to improve his game. What do you think is the best way to do that?
Personally I think reading books is a good way to get the basics: rules, hand ranking, starting hand selection, basic strategy. I also think playing online is a good way to cram in experience as long as there is the understanding that there is probably more d0nk play online on average. It depends somewhat on stakes of course but I think you will on average find more players just doing stupid stuff than in a home game or casino.
But once you have the basics concepts and math down, I think that to get to the "next level" requires feedback on specific hands. For me, the WNP/TuNP crew is the best way for me to continue learning when we discuss hands in person, email, or blog. I think that everyone here brings different perspectives on how a hand should be played. Marsh will tell you what aggression will buy you. Ryan can be counted on saying what the numbers tell you. Jason will tell you...the unorthodox play. And taken together I think that that all adds up to even having a single dedicated coach because seeing the different approaches gives you more options.
That's the best way I've found to keep improving my game at least.