I tried out a HAT spec today as well. We did a 10 man Naxx with a druid tank and no other melee buffs aside from the 5% crit, so damage potential was actually alot lower then it would have been if there were to be a warrior sundering or any form of melee haste. I stacked my group with an ele shammy, hunter, and 2 mages. The combo point generation was ridiculous after about 5 or 10 seconds into the fight. Very sporadic at points like the OP mentioned, but I believe this may be "somewhat" leveled out in a 25 man raid with more potential buffs. My overall dps was pretty low due to not fully understanding the build or having any set rotation, but I believe that with practice and knowing what to look for and when is going to be key in this build, and frankly I did not know my head from my ass walking into 10 man naxx with this build. Build during raid:
Talent Calculator - World of Warcraft
From my findings and experiences(limited as they may be), the potential dps of this build is absolutely insane. It does require alot of attention towards your energy bar..probably more so then usual for combat/assassination rogues. I found myself out of energy with 5 combo points many times throughout the night, and I would just sit there auto attacking waiting for energy to go back up. Not having the increased energy regen from vitality or focused attacks really can put a hampering on dps if you don't spend your energy wisely. So as Apps said it's very important to not get ahead of yourself and end up without any energy left to spend on finishers.
As for weapon choices I was running
[Calamity's Grasp] [Omen of Ruin]. Wound/Deadly. Although, with the amount of finishers I was throwing out, and the general lack of using Hemo, it may be more advisable to do more of a mutilate setup with two fast daggers and Wound/Wound.
For those who haven't seen the potential dps that this build can throw out, check out this wws.
Wow Web Stats
The other talents and abilities the HAT spec entails are things like Vanish for master of subtlety, and shadowstep for the increased damage on next attack. As for how those are used, my guess is that it's Vanish>ShS>Garrote. Or at least that's how it jumped out at me initially. With prep that combo is/could be used a few times throughout the fight.(Could be wrong on how these tools are used though.)
My foresight tells me this is one of those builds thats going to improve leaps and bounds as gearing improves overall and things like crit, hit, and group composition become more consistent. I'll try this out again next week for 25 man raids and try to report on any findings or changes that I see in 25 man raiding. I'm sure it'll only get better.