As I noted in a earlier post I have switched to using Server 2008 as my main OS and configured it so that I can boot with or without the Hypervisor enabled.
Today I got round to installing SP2 and after the machine came back up it felt sluggish, as though the Hypervisor was enabled which is odd as my default boot configuration has it disabled.
A quick check of my boot config showed that the service pack had reset 'hypervisorlaunchtype' to 'Auto' for all entries 
Very annoying but easliy fixed...
The other issue I've had is that the SP install removed 'Windows Mail' from my quick launch bar. Also annoying but easliy fixed.