C'mon now Rick.
A guy named Imagemaster who frequents other forums seems to get quite good results from the Tamron at 600mm. It isn't a Canon supertele, but it doesn't cost over $10,000 either. It offers a level of quality at a cost point.
I don't want to go on a cost crusade or anything here, but $1,000 for average Joe photographer is near the upper cost limit for a lens. At its $1,069 price the Tamron offers people who previously couldn't afford the entry cost for wild life shots. In the hands of someone as skilled as Imagemaster the lens can deliver really good shots at 600mm.
The Canon 100-400 II appears to be a great lens. And at its asking price it should be. It should take the Tamron behind the wood shed.
Dave