When I've done the latest update I get the message (appearing twice) that N-Mon.kext can't be installed and I should contact the vendor.
This has happened each time I've updated on two separate bootable partitions I use.
It has not happened on a fresh OSX install on a third partition that had no additional software and where I went straight from 10.6.3 to 10.6.6, only on the ones that had a version of 10.6.6 that was downloaded recently and lots of software.
Is it anything to worry about..? Everything (so far) seems to work ok.
17" MacBook Pro 5.2, Mac OS X (10.6.6), G-Tech external hard drives