+1. I would love to develop some customizations on top of GMail, but haven't seen a good explanation of how to do it (yet). Maybe I just haven't looked closely

+1. I would love to develop some customizations on top of GMail, but haven't seen a good explanation of how to do it (yet). Maybe I just haven't looked closely enough...but is this something Google actively encourages or something you have to mangle with a plugin like greasemonkey?