Windows 7: High CPU usage due to system interrupts (Deferred procedure calls and interrupt service routines)
Windows 7, much as I enjoy using it (although the shine has worn off a li'l bit), has a few niggles. One of these, which really annoyed me was the sudden seemingly random spike in CPU usage that, once it occurred, never went away until I rebooted the system. The task manager did not list any application as consuming any significant attention from the CPU. However, the resource monitor (which can be reached from the performance tab in the task manager) provided the answer as I found the innocuous sounding "system interrupts" process consuming a steady 40-45% CPU.