Microsoft community mouthpiece Larry Hryb has announced that Xbox Live will be down for a little whiles tonight (some are indeed complaining it's already down). Reason? Scheduled maintenance, that'll run from midnight to 0200 PST (make your own local time/date adjustments). Xbox.com will be down at midnight, Xbox Live itself from 0100, so if everything goes according to plan you'll only lose an hour. Take the time to re-acquaint yourselves with loved ones, or perhaps a long-neglected family pet.
PS - Hryb is adamant this is only for maintenance. No updates. Especially no dash updates. Xbox Live Maintenance (11/13) [Microsoft]