If you run Windows 7 and Linux on the same PC, you might run into an odd error when you try to install Windows 7 Service Pack 1. I've already had three readers contact me with reports that they were stopped by error 0x800f0a12 during the installation process. It's a non-fatal error, but still baffling.
The error is documented here, but you'll have to dig deeper to find the solution. A Microsoft support engineer has already posted the details of the problem and an easy fix. In all of the cases I heard about, the reason for the error is a check that the service pack installer performs. When it determines that the active partition is not able to start Windows directly, it produces the error message.
The fix, according to this report, is to use Windows Disk Management to set the System Reserved partition as active; if there's no System Reserved partition, set the Windows volume as active.
After this fix is made, you should be able to run the SP1 installer.
If you've run across this error (I haven't seen it personally), let me know in the comments.