I'm having the problem that the guest's clock is stopped on suspension but not set to the host's time after resuming. This is relevant for example when I build code from the guest that's on the host's share -- file changes are in the future. Easily fixed by setting the time in the guest but it would be nice if the hardware clock could be set on resuming instead.
On linux ... I notice the same thing. I don't have a fix for Windows, but on linux I run # hwclock --hctosys directly after I wake up. I was going to figure out if I can cause a software suspend to work. I did this once on a OQO running linux, but didn't write down how I did it. I guess there must be an equivalent command in Windows to synch the hardware clock to the system clock ?
For Windows guest you should install Parallels Tools. One of its components - time synchrinization tool will synchronize guest time OS with primary OS time after resuming.