I agree that playing for free online is a lot different than playing for money. People play much much looser, I would call them maniacs. That being said, I think there are things you can learn from this kind of poker but you need to be very smart about it or you will be preparing yourself to lose a lot of money when you start playing for real.
I play a lot of free poker on pokerstars.net. I play for free because it is a felony in the state of Washington to play poker online for money. I also go to a casino a couple times a month and play in no-limit tournaments. I have won these on a couple of occations. When playing online, I play in the small no limit tournaments (9 to 45 players). Once you can build up enough points to play in the higher stakes tables, the play is much more solid than the lower stuff but is is still quite loose compared to playing for money.
I think I gain a couple of things from free online play. The first is to get a feeling for how well different hands play in different situations. For example, do I feel comfortable calling a 3xBB bet with 10-9 suited in the big blind late in a tournament? You need to play 1000s of hands to get a feel for those types of things.
The second is patience. If I can play patience solid poker in the free online tournaments, I can be one of the last people at the table all most every time. If I start playing a little sloppy, I am gone. The same holds true for when I play at the casino except it's not as easy to make it to the final table. One thing you cannot learn free online is how other people will play certain hands. Since there is no money involved, people will play anything.
So play just to get an understanding of how different hands hold up in different situations and to develop your own style to some extent but you must also learn the mind set of playing for money to have any chance of making money.
