Yeah, think I am canceling my order and waiting a bit. Just doesn't seem like it will be a significant upgrade to justify the money.
When you consider nVidia will be releasing the new chips in a month according to some sources and the 256mb 8800GT it might be a good idea to wait. Plus the 3850 may come down a bit in a month too.
No new chips, if anything a potential variant of the G92, but nothing else that would pique your fancy (65nm GF8400 interest you?).
Also I wouldn't count on a GF8800GTS-256 anytime soon if they can't meet 512 demand.
Main thing is what game you're interested in playing? The GT will give you playable features on most current an near term titles, so waiting's not a bad idea, but the target of that wait would need to be something more compelling because a GF8800GT-256 is no different than the HD3870 for an upgrade.
Only if you could get a refreshed GTS or better for a good price ratio would it be worth consiering any differently than the current options.