Using Fedora 7 host, Win XP guest, VMWare Workstation 6.0.1
On boot of the host and startup of the guest, VMWare Tools works great. Moving the mouse between the guest and the host works brilliantly with an almost instantaneous focus switch.
(I presume VMWare tools is responsible for this intelligent switching.)
After a couple of days, however, Tools seems to get tired of doing this little job. It gradually gets slower and slower in switching time. Eventually it becomes almost useless. It also seems to get a little lost about the mouse - sometimes thinking the mouse is still in the guest even though it's in the host.