I have the same problem, though slightly less.
No idea what causes it, either.
Top causes for wakeups:
63.0% (699.9) <interrupt> : acpi
System is Linux gentoo-pc 2.6.22-suspend2-r2 #13 SMP Mon Nov 5 18:19:59 CET 2007 i686 Intel(R) Core(TM)2 CPU T5500 @ 1.66GHz GenuineIntel GNU/Linux, running KDE3.5.
The problem only seems to happen in KDE.
Does anybody know?
<Edit> I went through a KDE startup manually, watching powertop. The problem seems to appear whenever anything related to ACPI is started, i.e. ksysguard or the taskbar applet. Doesn't go away when the respective program is closed though. Very weird.