You don't know what "no known issues" means. It means that the update doesn't cause any additional known bugs. It is not in any way saying that the operating system is 100% bug free. For example if they were working on an update to Quicktime, but they weren't yet finished, their changes might cause iMovie or iTunes to crash. This would be a known issue listed for that given build number of the update.
8/20/10 at 2:36pm