If you do a fresh install of Windows 7 these days? The update process is PAINFUL! You'll literally need to leave the PC downloading updates for a good 8-10 hours or more before it finally starts doing anything obvious.
That's why you slipstream updates into your installation image. Slipstreaming the various post-SP1 patch rollups as they're released will slash your installation time significantly, and there are only a relative handful of them at this point.
The only thing slipstreaming doesn't cover is updates to the