I think many virtual sites can be helpful if you want to try something or see how it works without using real money. Many of the social networking and game sites have several sites like these. I have also found that they can take up a lot of time if I am not careful.
I might sit down to play a game for 20 minutes and realize a couple hours have gone by. And you think, if that only was real money - all that I could do with it.