If this is the Twitter widget that is black, full-screen and is listed under widgets as "Twitter (HTC)" then mine is down too. I thought this was the official Twitter widget, but maybe it's the Friendstream Twitter widget? Actually, when I post a Twitter update, it says 'sent using Peep' or whatever, so it's apparently a Twitter app linked to Peep.
UPDATE: The widget I'm using is linked to Peep, so apparently not the official Twitter widget. Anyway, I finally fixed the problem. I loaded Peep instead of just the Twitter (HTC) widget, then cleared the cache, and voila my widget now works, shows updates.