I thought that at first aswell, but as it states here;
As Microsoft gears up to bring you the New Xbox Experience (NXE), Xbox LIVE and the Xbox LIVE page on Xbox.com will be down for 24 hours, beginning on September 29, 2008 from 12:01 AM PST until 11:59 PM PST. During this time you will not be able to access Xbox LIVE.
Note that this does NOT mean the NXE will be available on September 30th, this is prep work on the back end. Also, given their record, don't hold your breath for it to come up exactly at 11:59 PM. My personal opinion is that you can reasonably expect services to be up by noon the following day. For those with blogs on 360voice.com, their typical approach is to not count the 29th for streaks but streaks will not be interrupted due to the outage.