While researching the possibilities of the Infragistics NetAdvantage suite of controls, I noticed poor performance of the WinForms controls on Vista only. Basically, whenever the mouse was over a form that had an Infragistics control on it, the CPU went 100%.
A quick search on the Infragistics site lead to the Feb 9th Hot Fixes download. I downloaded and installed the Hot Fix 20063.1059 (38MB). The problem is now fixed with no CPU spikes on Vista.