I'm using PH 2.28 (r5073) on MSWindows XP SP3. Each time PH is started now, it reproducibly uses ca. 50% CPU time so that one core (of my dual core CPU) is fully utilised. This stops immediately after opening PH's main window. Using the PH tray icon's menu to view the properties of eg PH's own process does not make it stop.
I usually hibernate my system (and after being resumed like that, PH does not eat up CPU time like this) so PH isn't started often. I think that initially PH did not behave in this way though. I've been using it since 2012-09-06.