Are they quality, well marketed apps? We on WP7 are somewhat app-starved compared to other platforms, most people I know on WP7 download apps left and right as long as they know the app exists. Free versions with ads alongside a premium version without ads seem to do very well, and gain money no matter what.

A big problem I've had is finding an app exists and being surprised that it exists. If it doesn't get advertised, there's no way to know it's there.