Diablo 3 will go offline in a few hours for scheduled maintenence - but it's probably worth it. The servers come down at 3:00AM PDT with all services to resume by 1:00PM PDT. Not all region's servers will be down for this entire period, though; the maintenance is scattered by territory, and you can check when your locale goes dark on the RPG's forum. Note that Global Play will be unavailable while other regions are updating. See the patch notes here.
Thanks, Blue's News.