I've never been disappointed with D&D as a whole upon release of a new edition (I've been around since late 1E), so I'll certainly be picking up the 4E PHB.
Now, if it rocks my socks, I'll start fresh: new campaign and all.
If it's a good game, but awfully different from what I expect, I've still got plenty of 3.5 stuff to run (WLD, City of Brass, Pathfinder, Dungeon Magazine, etc.) and will relegate 4E to "whenever we want to play something else."
If it stinks (which I *highly* doubt), I'll suffer the loss and keep the PHB in case I want to play it later, or to mine ideas from.
If it's anything like the Wildside Fantasy Role Play* system, I'll track down the designers and kill every last one of them.
*If you've never heard of this, you're a very, very lucky person.