Here's a pretty good introduction: http://diveintomark.org/archives/2003/04/21/whats_your_winer... (read the comments)
He has a long history of fucking over business partners and customers, developing mediocre ball-of-mud software, writing terrible specifications and being the worst spec-maintainer of all time. Thankfully most of his technical efforts have been unsuccessful, despite the effect his self-aggrandizement had on the media for much of the last decade.
Unfortunately a few of his clusterfucks did slip out: XML-RPC, SOAP, and his epic mismanagement of RSS (which only ended with a headshot from Atom). The man singlehandedly set the web's progress back about a decade! If not for him, the nightmare of WS-* would not have existed -- the likes of Microsoft and IBM would have done something stupid in a big way, but they wouldn't have pretended it had anything to do with the web.