A few areas to watch:

- 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.

Specific examples. Consider them anecdotal but if you run any software mentioned here, or similar software, this list should give you a guide to test.

• Users with old versions of Microsoft Security Essentials may not be able to install SP1. Upgrade first.
• Samsung Galaxy S phone drivers may have problems with SP1
• some users reported very long install times (> 1hr. but not all that unusual for a service pack)
• Chrome 10 and 11 have issues according to some tweets
• Word 2003 VBA
• slower boot times with SP1 then without
• some reports of download issues due to overloaded servers
• Lenovo's Thinkvantage System Update may not work (update it before applying the SP)
• EVGA Precision Utility 2.0.2 (Graphics card stats program liked by gamers)
• MSI Afterburner
• some issues with Bitlocker are reported. But no confirmation at this point and it may also be due to entering the wrong password on reboot (you have to reboot a couple times in certain situations)

Link to a technet page with reports of install issues:

http://technet.microsoft.com/en-us/library/ff817622%28WS.10%29.aspx

If all fails, here a link with an uninstall procedure for SP1:

http://windows.microsoft.com/en-US/windows7/uninstall-sp1

To temporarily block installation of the service pack:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=d7c9a07a-5267-4bd6-87d0-e2a72099edb7&displaylang=en