Not that great for $300. It's faster than the 5950U, especially in DX9 games, but not enough to justify the price premium over a flashed 5900 -> 5950. IMO, it would be a nice deal for $250.
A few days ago best buy had a preorder for the BFG 6800GT OC (370/1000 vs 400/1100 for the 6800 Ultra, both 16 pipeline NV40 cores) for $300. That was a relatively good deal for a new video card at introduction.
If you already have something decent (9800 or FX 5900) and don't really want to spend $300 for a new card, just wait a couple of months for the price to drop.
yeah its pretty good card, but for the price its not much better than a 9800xt or 5950U. i think it really showed up the 5950U in games like splinter cell, tomb raider, far cry (without aa/af). the overclocking isnt too great. but for a msrp of 300 it isnt terrible, cause that 256mb 9800pro on newegg is around 300. they should of had 256mb of memory on it.
as said above a GT or Pro is a better buy, more worth it at just 100 more.