I just compiled 2.6.11 from 2.6.10 config using 'make oldconfig',
activate new options to default values (i.e. set "main kernel lock
preemtive" to YES).

Booting X in new kernel makes my touchpad very unresponsive. I can't
click any longer in the touchpad area, and the touchpad doesn't response
when moving in small increments, so the whole experience is quite bad.

Attached Xorg log, may be of use.

2.6.10 worked ok in this respect, as 2.4.27.