There are a couple times where play money games are valuable. The first is to see if you like the interface and to get used to it if you like it. I played hundreds of hands on UB with play money before I decided that I liked it enough to put money into it. I played play money at pacific poker and hated the interface so much I decided I didn't want to play there.

I've also found that the tournement games can be somewhat realistic. If anything, play these. The play money ring games are an absolute joke though. It's a totally different game...but if you want to get technical, you should be able to beat the play money ring games too. You need to use a different strategy to win though, so the experience isn't worth much.