I rebooted and Htop is still showing 86.9% usage despite not running any applications.

Did not do a recent firmware update. Although I am in the UK I bought my N900 in the US and updated ages ago when the rest of the world got the update.

One thing I just thought to try is a hard reset. Will see if that helps. If not I guess I would have to reflash the device.

Edit: Wow CPU just went up to 100% for a second.