The GTX480 retails at $500 before its inevitable price drop, while the 5870 retails at ~$420. The 480 performs noticeably better.
Regardless if the 28% increase is true, it will be a better buy when stocks are increased.
I'm not sure you read my post correctly. The GTX 480 has an MSRP of $500. This will almost certainly increase $50 to $100 for the next few months until supply/demand meet up. Even if it were to be sufficiently available at $500, it still does not have any where near the performance increase to justify the additional $80-$100 cost.
Lets check out some performance comparisons...



It should be noted that [H]ardOCP doesn't use canned, pre-recorded benchmarks for testing and actually plays through a chosen level to gain real world performance statistics.
How about we check out a different site? Lets try Tom's hardware...





The results above leave a little more to talk about than the [H] benchmarks. Starting at the top, The GTX480 wins by a landslide in MW2. This advantage, whilst impressive, is rather pointless as you aren't going to see the benefits of 120FPS vs. 70 FPS. With Dirt 2 the GTX 480 eeks out a minor 5FPS without AA, and roughly 10 with AA. In Crysis, the HD5870 out does the 480 very slightly without AA, and only falls about 3FPS behind it with AA, both are unplayable at this resolution however. Stalker shows a similar situation in which the 5870 outperforms the 480 w/o AA but falls behind the 480 with AA enabled. Metro2033 is quite unique in that it brings a few special features to the DX11 table that quite simply crush any modern GPU. The GTX 480 isn't even playable with this enabled and is a no go for ATI GPUs. You'll note that in [H]'s review that feature was disabled and we see almost identical performance from the two GPUs.
The point still stands; in certain games with AA enabled the GTX480 pulls ahead by a small margin. This margin is far too insignificant to justify spending an extra $80-$150 on for the savvy purchaser. The 5870 is widely available in a variety of flavors at an acceptable price point and can play modern games at the highest settings with great performance. If you are in the market right now for a GPU and you don't demand the absolute "king" of performance, the HD5870 is the wisest choice. If you must have that extra smidgeon of performance, or really want Physx/CUDA, and don't mind spending $100's extra, and don't mind trawling the internet for hours and days at a time trying to find it in stock, and don't mind the enormous power consumption and heat production, then yes, by all means attempt to purchase a GTX480.
In 6 months time it may be a better buy. But then you'll have to consider whatever refresh ATI comes out with. In any case, Ephi is trying to buy a computer soon and the GTX480 is not the best choice right now.