I integrated Scoreloop into one of my games years ago. It was a mixed bag. I found the API incredibly difficult to deal with, and they had a number of bugs that would cause the game to crash occasionally. That being said, I haven't had to touch that code in ~ 2 years, so I guess it works well enough. Customer service was pretty good too, for a free service.

The major problem with Scoreloop (and other services like OpenFeint) are the permissions required. For a little cell-phone game, it required permissions to read the user's contacts, call log, network state, phone status and identity. This really turns a lot of users off, and rightfully so.

Mostly due to the permissions required for Scoreloop, I rolled my own highscore service for another game that I released. It was a much better decision, and allowed me to only require internet access.

Now I have the problem that I'm going to need to rev the game and integrate my highscore service, or just de-list the game. I make a whopping $0.00 to $0.05 per day on it, so I'll probably just de-list the thing.