I frequently grab/ungrab the mouse in my game. It works great under the right circumstances, but it has a few major disadvantages.
For example, it doesn't work at all if the game is on a secondary monitor. The game just locks up until I release the mouse.
On linux, it sometimes causes the game to not receive any more keyboard events, ever. The actual mouse grabbing problem seems to have been fixed in 2.2.2, though.
Since the mouse is released on a keyboard event, not getting keyboard focus is a bit of a problem.
I switched back to using Robot and MousePointerInfo, but that doesn't play well since it's multithreaded and unpredictable (it sometimes leaks coordinates because it's not synchronized), and it's really slow on some systems.
I'd pay to get this fixed.