I've never heard of a limit, but I've got the free one. I got it ages ago though, so maybe that's why I don't have a limit.
It's no good for proper and/or background listening, assuming you don't get the paid one, because there's annoying ads every few songs. However they only play after songs end, so it's perfect if someone's mentioned a new band. You can have a quick listen through a few of their songs, and if you click the next one before the one you're listening to ends the ads don't play.
Basically I use it as a "try before you buy" kind of thing for music. It also lists similar artists to whatever band's page you're on, and I've found a couple of new bands this way.
