Forever I have been one who has/had no problem with play money poker. PM (Play money) and public freerolls staked me to my first real money games. Actually it was the public freerolls (party poker).
The major difference in play vs real money games is the scared money aspect of poker. You are never worried about blowing your whole wad at a play money table. The one counter to that is if you substitute pride for fear. If you set a goal of accumulating some ungodly amount of play money chips in your play money bankroll, you somewhat approximate the scared money aspect of real money poker .
I still maintain that there is a rough approximation between the play at the highest levels of play money games and real money stakes at the higher micro levels ($5 & $10 sng's/MTT's).
What you can learn at play money is reading players via their betting patterns. Not what they play, but how they play. At some point you start taking notes, and this will be good when you run into those same players later when you are both moving into real money poker.
But do not think you can learn about starting ranges, or position play, or sophisticated moves without some consequences. That is where the scared money aspect forces you to really learn the game.
So, while I support learning as much as you can freely, I also now realize that what you can learn is more limited than what I used to think I could learn via play money poker.
Best idea is to get into our freeroll club, and play the best prize pots around with the fewest players. Many will 2nd and 3rd this notion, and few if any will say it is a wrong move to make.