Ran into an interesting problem where a WPF application was acting really, really, really slow. So slow that moving the application window was jumpy. Selecting items in a grid would take several seconds. Scrolling a list box of simple items would grind the CPUs for a while. And even typing in a regular text box was so delayed that I could type a word, sit back, and every few seconds a character would appear.
The problem turned out to be with the input stack at the operating system. Seems that the Pen / Tablet Driver was bringing the system to its knees, but only affecting WPF applications.
Disabling the driver and restarting the WPF application instantly showed colossal speed improvements for response time; the application responded near instantly. Re-enabling the driver while the application was running reverted the system to the broken state, although turning the driver back off did not bring the WPF application out of it’s slow like crawl. Restarting the WPF application resolved the problem, but the driver had to be disabled.
(Test conducted with WPF 3.5 SP 1 and Windows 7.)