I've also used bumblebee and am generally quite happy with it. But the big drawback of bumblebee over a "proper" implementation is that the rendered frames are

I've also used bumblebee and am generally quite happy with it. But the big drawback of bumblebee over a "proper" implementation is that the rendered frames are copied to the Intel GPU in software. I hope that Dave Airlie's work on hotplug will lead to a better implementation at some point.