Exchange 5.5 can be a touchy beast. Our server lost power and shutdown without going through the Shutdown process. This is apparently very bad for a machine running Exchange 5.5. It took about two hours of running diagnostics, recovery utilities, test packages, and praying really hard to get the Information Store service to start-up again. Apparently when the service gets shutdown without writing the last log file, very messy things happen. I hear Exchange 2000 is better at this.