Looks like the openSUSE build service can package up your software for a bunch of different Linux distributions, cross-compile, track upstream project dependencies (e.g. rebuild your GTK app when GTK changes), and runs on their servers so you don't have to maintain the thing.

Add in Windows and Mac support and they might have something there :P

This might be a great idea for a higher-level "cloud computing" service, setting up and maintaining this kind of infrastructure is a huge problem for many companies.