We had a strange RS experience at one of our customer sites. It looked like the Report Server windows service started executing ExpireExecutionLogEntries stored procedure in an infinite loop, it was getting kicked off every few milliseconds. The CPU usage was close to 100% for a few hours, affecting the server pretty badly. Stopping the service made it go away, but it resumed when we restarted it. I searched the newsgroups and found a post about the same issue, followed by a response from Microsoft, saying "We have seen the issue and we are looking into the cause". The issue finally went away after rebooting the server. If anybody from the RS teams reads this - I'd be more than happy to help you figure out the cause and collect data from the server if needed.