It sounds like a fun concept, but it's still just a game. Real-life investing is a lot different. First of all, you're "playing" with real money, and most people are too impulsive and impatient: they buy on the hype (current gold craze, anybody?), sell whenever the price dips, panic easily, don't think long-term, etc. It's easy to stay cool when you know you're trading "funny money" and it won't affect your livelihood in any way. And then, of course, there's the 3-day waiting period for your funds to clear after you execute a trade (unless you're trading on margin, in which case, IIRC, it's only 1 business day). And who can forget about the Day Pattern Trading brought to you by the beloved SEC? I.e., if you have less than $25,000 in your trading account, you're a horrible, irresponsible and probably dumb human being and should not be allowed to do more than 3 day-trades per week.
So yes, this is definitely a fun game - but it's just a game. I daresay that the real market is a lot more difficult.