I recently installed Windows 7. This was a clean install (i.e. not an upgrade from another version of Windows), but I did install a bunch of other programs. All mainstream applications - nothing wacky.
Since then, my CPU usage has been constantly at around 50%.
Task Manager shows me that ngen.exe is the culprit. It's not a long-running task: I can see that it gets a new PID at least once a second, so I guess something is constantly triggering it.
It does it all the time, even when I have no applications running.
Has anyone else seen this? How do I find out what's causing this?