Wow, some serious arguing going on here. I thought I would add some info into the mix without going fanboyish in any way.
First, the 3850 is meant to compete with the 8600gts. It should be priced around the same, yet hopefully deliver the performance of the HD 2900GT with 1/2 the power consumption, only have a 6 pin pcie power connector (instead of 1 8 pin), and be single slot cooled. As those graphs illustrate, the 3850 dominates the 8600gts. I would then expect the HD 2600 series to become the low end ATI cards, and the HD 2400 series to become integrated into motherboards.
It is the HD 3870 whose job is to compete with the 8800GT, not the 3850. Don't confuse the two! I don't know much about the 3870 (therefore I cannot say if it will have half the power consumption as the 2900xt, or what power connectors it will use), but it does seem that it will retain a dual slot cooler. Note: dual slot cooler != running extremely hot. Also, how will the performance of this card be? I don't believe any of us are in a position to answer that beyond speculation. I will be interested to see cooling and noise benchmarks of the slot coolers for the HD 38xx vs 8800GT when they are all out on the market.
As for current cards, it seems that with up to date drivers, HD 2900XT gDDR3 roughly compares pretty well with the 8800GTS 640mb (it beats it in some tests, looses in others, but they roughly match out to the same are in the same pricing arena). The 8800GTX/Ultra typically dominate all their competitors. Whoppity-doo, do you expect any less from the prices being asked for them?! The 8800GT seems to perform above the 8800gts 640mb, but below the 8800GTX, yet costs much less.
Also to add, to know just how closely related the HD 38xx series is to the HD 2900XT, pay attention to the performance of the cards after AA is enabled. The 2900XT seems to become less competitive after doing that. If the newer ones don't, then they are probably more than just the "R600" die shrink Nvidia fanboys are claiming it to be.
Finally, if you remember, when the 8800 series first came out, purchasers of it liked to gloat against ATI owners because they had DirectX 10 support when they didn't. However, how long afterwards was the first DirectX 10 game released that wasn't just a patched DirectX 9 game? After the HD 2900XT, launch, that is for sure. Therefore, I believe history will repeat itself with select ATI owners gloating about having DirectX 10.1 support while Nvidia owners don't, when the first decent DirectX 10.1 games probably won't be released before Nvidia releases their own DirectX 10.1 card (something even further evidenced by the increasing "The Way It's Meant to be Played" campaign).
End of rant...
Edit: Sorry to add more... I don't believe the 3870 will have two cores/be crossfire on a card. I think that will be a separate card called the 3870x2. Also, ATI will continue to dominate in the AGP market, which refuses to go away.