If you use AVG, this is important. A recent update to AVG 2011, 271.1.1/3292 (432/3292) causes 64-bit versions of Windows 7 to fail on restart with the message:
STOP: c0000135 The program can't start because %hs is missing from your computer. Try reinstalling the program to fix this problem.
On AVG's website, information about this and a workaround are available.
According to that page, the 3292 update has been downgraded to 3291, so if you don't have the 3292 update you should be good. You should double-check the update that AVG is on before restarting, though, just in case.
[update: A fix is available.]