Level 80 premades are now available on beta, and apparently Naxx is going to be available for testing "soon". Blizzard post from today:
The trash has indeed been adjusted. Highlights include:
Longer trash sections between bosses ( to Patchwerk, to Razuvious, to Faerlina) have been toned down.
Heigan gauntlet is no longer a gauntlet, now there's a very small one AFTER Heigan.
A few new creatures have been added in a couple places.
Newer models for many of the creatures.
Some of the trash encounters have different numbers of creatures for 10 and 25 player modes.
One other thing...
Naxxramas should be available for beta testing soon in both 10 and 25 player flavors, including loot!
MMO Champion reports on premades:
All characters are level 80 with 4x22 or 4x20 slot bags depending on classes, PvP gear including full set of weapons, an epic flying and ground mount. Exalted with one or two faction depending on classes and friendly with the rest, maxed weapon skills and First Aid. Gear is also fully enchanted.
Additionally Jagiya posted some encounter specific stuff in the WotLK thread:
So now that those fellows over at Premonition have begun privately exploring/datamining Naxx data (not sure which method, but it's available), it's good to see that Blizzard went through with the 2x Obedience Crystals for Razuvious, meaning you can MC the adds with any class/composition.
Additionally, they managed to score the HP values of each of the bosses in 10 man Naxx. Of course it's safe to assume that these values will be changed during several phases of testing and balancing, but at this point, it seems that you require 11,286 Raid DPS to defeat Patchwerk(10) before the enrage timer; assuming it stays at 7 minutes. I'm really doubting that they'll require more than 2 tanks for this fight; as to adhere to their "flexible" raid options attitude; so assuming you're bringing 2 tanks and 3 healers, you're gonna need around 2258 DPS from each raid member to kill 10-man Patchwerk. Assuming you're good enough to do it with only 2 healers, then you can get away with 1881 DPS per person.
It'll be interesting to see how much tuning takes place, and how difficult they want Naxx to be as an entry level 10 man dungeon. At a glance, you'd look at those numbers and think, "we're already capable of pulling those numbers in Sunwell" (circumstances allowing for stacking and consumables/buffs), so it doesn't really appear to be a huge "gear check." By the looks of it, it'll be somewhat trivial for the Sunwell veterans, but still challenging for the "not-so-hardcore" population.
I'm really curious to get my hands on the 25 man data and see what sort of numbers are expected... but again, it's somewhat pointless to speculate at this point, given how many changes are yet to be made.