Yes I have a similar problem, with several Orbits...
We have developed our own app for these, but after sometime - could be days or weeks, the PDA will just go so slow within Windows, even when our software isn't running.
Theres nothing I can see thats obviously wrong, and I know that a hard reset will fix this.
Are there any diagnostic tools out there for PPC, or something that could help us get to the bottom of this?
Using WM5.0 O2 rom - I think there are other Orbits with the same problem that are using WM6/wm6.1 - still the O2 rom though..