If you haven't had the pleasure of patching WSS 3.0 or MOSS2007, you're missing a real fun experience. If you are one of the folks who've had to go through the pain, there's some good news for you. If you're particularly adept at reading KB articles, you might have noticed this little tidbit in 953749.
"Improvements to the time that is required to update and upgrade Windows SharePoint Services sites."
Starting with the release of the Infrastructure Updates, we've changed the patching process a bit. Each time a patch was applied, we followed all of the upgrade sequences to perform a build to build upgrade to get an install to the latest version. One of these sequences is the site collection upgrade sequence. This sequence went out and touched all site collections, even if it was to just update the build number. With the IU, we no longer do this. We'll only call this upgrade sequence if there are changes that need to be made to the schema that affect site collections. (Touching every site collection was a very time intensive process) This is the good news.
However, this is only part of the picture. While this may show some improvement, it's not the end all of fixes. If you're only performing major service pack patching, this is highly unlikely to save you any time, as there are likely to be object level schema changes. The real benefit will be for applying QFE and CU updates. It also needs to be said that SharePoint (WSS and MOSS) patches are cumulative, so if you think you're only applying a recent QFE/CU, you are indeed getting all the fixes between your currently installed build and the the build of what you're patching to.
As always, different environments will perform differently. In order to get accurate estimates as to how long patching will take for you, you're going to need to test with a copy of production data in a test environment.
Patching is a very confusing process for most customers. Please do not hesitate to contact Premier Support for guidance. That's what we're here for.