Dan Drezner is subbing for Andrew Sullivan on Sullivan's blog, the Daily Dish. Yes, Sullivan's blog has a name - it's just that nobody remembers it, so he's universally linked by his name, instead of by the blog name. It helps that he was a nationally-known journalist and columnist long before blogging took off. He's Andrew Sullivan, while Glenn Reynolds is still universally the Instapundit.
Anyways, Drezner is covering for Sullivan. Drezner is a substantial blogger and columnist in his own right, so that's a tad odd. He's having great fun with the gig, though. He's running a stream-of-consciousness log on his own blog, discussing the thinking behind his turn at Being Andrew Sullivan.