We've been hearing plenty of reports throughout the day of patchy access to the new Xbox Live marketplace following this morning's launch of NXE, as has Kotaku.
The problems have been occurring for both the website and 360 interfaces.
The UI update his another snag in the form of US users not being able to access Netflix, one of the upgrade's main features, but, according to this Nelson post, the problem's been resolved.
Aside from that, there doesn't appear to be any other major hiccup with the NXE roll-out. So big hugs all round.