Okay, now that everyone told you how bad play money games are I'll tell you that it's not entirely true. Many of the people you'll see on play money tables are Americans who can not play for real money. Does this mean they play bad poker? Not really. Then there are the people who enjoy the risk-free element of play money games but still play a good game.
Yes, there are a lot of bad players but they are also in real money games. These days it is not so easy to get play money on
pokerstars anymore so people tend to value what they have. You only get 12500 chips every 4 hours and the minimum buy-in for a cash game or any tournament is 10K. So if you play stupid you're out for 4 hours. Most people learn this very fast and start to at least try and play better. Those who don't will be sitting and waiting for their 4 hours to pass quite often. Of course some will load up a few times over a few days before wasting it all with bad play but the really bad players usually don't wait that long.
If you plan on making it on real money tables then yes, you'll need to play real money games. Not because play money players are all bad or teach you bad habits but simply because you need to get use to the risks and learn to calm your nerves and apply proper
bankroll management. If you have the cash to play with then by all means move to real cash. But if you don't then there's no shame in honing your skills on play money tables while you wait for the next free-roll.
If fact, if you can beat play-money tournaments consistently you'll find it's not so different from free-roll and micro tournaments. You get your bingo players early on and if you survive then you end up with the better players after the first hour or two.
And let me tell you, you haven't seen more serious players than those who play at the 1M+ play money buy-in levels.