Is it just on my machine or is the Windows mouse acceleration being taken into account when it's in "grabbed" mode? I saw the changes in the ChangeLog but I'm not sure if this is intended. Until now I was doing my own mouse acceleration to compensate because in the "grabbed" mode the cursor was much slower.
This is expected, since we've gone from using directinput to using windows messages for input, which takes configuration parameters like mouse acceleration into account. The downside is that this is a change from previous LWJGL versions, the upside is that the mouse should now be consistent on all platforms (since acceleration is applied on mac and linux LWJGL input).
@princec: The directinput->windows messages work was needed because multiple mice through JInput don't work when DirectInput is active (this is an inherent flaw in the windows implementation of Raw Input and DirectInput). The non-direct buffer support was inspired because I realized they could be supported with very little (and constant) code size overhead and no performance overhead.