As of [1], there's a new non-optional dependency. In addition, the package now uses INPUT_PROP_SEMI_MT from linux-headers' input.h. Version sys-kernel/linux-headers-2.6.36.1 was not enough, 3.1 works OK. [1] http://cgit.freedesktop.org/xorg/driver/xf86-input-synaptics/commit/?id=fadf9cf5e8659ca8500faac498327e6cadcd2652
Thanks, fixed.