this happened to me once to, with the NOKIA logo with white background on startup, and a small black box that says UPDATING below it. but it happened only once. no reboots after that.

have you installed NitDroid? or FCAM?
what app exactly did you update when this all started?
what is the power kernel you are using? and what version?
could you post desktop screenshots maybe? or a TOP result in x-term?