Hm, actually, this might be a good project for me. I recently figured out how to intertwine Torque, Java, and SQL. This means I could make a client-sided add-on that gives you achievements, then tells the server I make in Java you got an achievement. It would then be submitted to the SQL database so it remembers which achievements you got and other people could view them via some method (maybe a .php page, I dunno).
The problem that's come up every time this is suggested though is that it is VERY easy to hack client-sided. Some guy copies and pastes the achievement code into loops and releases it.