I actually disagree with a lot of the people saying that play money is a waste of time, as while it may not teach you much about poker techniques against the typical poker player, you can still learn about the concept of bankroll management, going on tilt, how to play against loose opponents, etc. Of course, this requires that you don't stoop to the level of your opponents, and take the play money games seriously. However, there is a major caveat in play money, at least in my opinion. Ring play money games do very frequently turn into all-in fests where any hand goes. People might take them more seriously at higher blind levels, some others may not. I believe you can find a better quality of competition in play money tournaments and multitable sit-n-gos. The first few players that are eliminated are usually done with all-ins, but by the time they are gone, the competition is usually taken more seriously. In the larger tournaments, many players will sit-out or give up for the interest of time, but if you have played into the end stages of a tournament, you will find players taking the game more seriously, plus you will test your resolve against fishy and loose opponents in the early stages. I would argue that play money multi-table tournaments are equivalent in terms of play to a freeroll tourney. Obviously, as multiple posters above mentioned, the best kind of experience for play money would be the Home Games on Poker Stars, as people there take the competition seriously (look at the leaderboards lol), and play in them as if they were real money games. But don't expect to jump to money games and make huge profits obviously. Hope for the best, but have realistic expectations and expect the worst.
Source: Been playing play money for 7 years, and still having fun with it.