In a not entirely surprising development, the folks at the SANS Internet Storm Center are getting a number of reports of problems with Service Pack 1 for Windows 7 and Windows Server 2008 Release 2. The most common problem areas are:
– Whitelisting / Blacklisting: Whitelisting software may not have checksums yet to verify all the files that are modified by the service pack. Same for anti-virus: Some anti virus products monitor system files for changes and may sound an alert or block the installation of SP 1
– Firewalls: Third party firewalls may find that some of the low level hooks they use have changed.
– Disk Encryption: In particular full disk encryption that modifies the boot process may find that some of the changes it did are undone by the SP install
– Custom hardware: If you are using drivers other then those that are included in Windows 7 (or 2008 R2), be careful.
There is more detail in the SANS article, and at this Microsoft TechNet page.