I saw this tip posted by someone from Microsoft on a forum recently so I thought I'd call it out here too. If you are applying one of the update rollups to your Exchange 2007 installation and you have any issues, note that you can increase the logging produced by the installer by adding a few extra bits to the command line. For example, take this command to install Update Rollup 5 for Exchange 2007 SP1:
Exchange2007-KB953467-x64-en.msp /lxv* c:\953467.log
This creates a detailed log file called c:\953467.log (or whatever you want to call it of course). On my test lab, I installed Update Rollup 5 and noted after the installation that it created a whopping 46MB log file. Now, I'm not saying you will need to know or even understand everything in the log, but it could help to shed some light on why the problem has happened. Or, perhaps the PSS engineer assigned to your call will request this file anyway. :)
The picture below should give you an idea of the output.