I could be wrong but I'm sure i read somewhere that the energy regen would replace white damage speed increase but I can't seem to find where it was.... either way I'm not suggesting that haste wont be good, just that it could be less attractive to mutilate than it is currently.

Further down that thread is the kicker.

World of Warcraft - English (NA) Forums -> Cataclysm Stat & System Changes

If it really becomes a problem, I imagine the easiest solution would be to make Eviscerate behave like Ferocious Bite (base cost 35 energy, plus anything more turns into bonus damage).

Alternately, one could try to avoid timing AR such that it overlaps with melee attack speed buffs (which increase Combat Potency gains). I already run into issues with this on the LK pull when I get the DBW Haste proc and already have Bloodlust + Blade Flurry + Potion of Speed + AR up.

I don't think we're in any particular danger of having "too much" energy in the sense of not physically being able to spend all the energy we're regenerating. I can conceive of it happening during AR, but I'm not honestly that worried about that situation. It's a DPS cooldown; if you have to time it's usage well and spam like crazy to minimize the amount of it you waste, so be it. And outside of AR... I mean, the standard combat cycle uses at least 35 energy per second, and even with Vitality and Combat potency that's well out of the reach of any amount of haste you're actually going to obtain. So it's not like we're going to have serious issues with not being able to keep up, outside AR and perhaps the occasional RNG spike.

And, at some level, it's fine that the class is spammy. I don't remember where it was, precisely, but I'm pretty sure I read something from Blizzard asserting that rogues were supposed to be the class that required the most input spam to play, and if we're being realistic most of us spam way more often that we actually perform moves anyway. So it's not really a bad thing that we're going to get up into the range of doing a move every 2 seconds.

The problem, as I see it, is that energy regen *is* getting to a point where we start to lose some of our class-defining identity. At current, we're one of the very few classes that is resource limited rather than time limited in terms of our DPS cycle. That is: what controls the rate at which a boomkin deals out damage is generally not their mana pool, but the simple fact that moves have cast times and they're basically casting full time all the time. Ret Paladins are not limited by mana, but by what moves are off cooldown for them to do at any given moment. That is: many if not most classes are limited in their DPS cycle by the fact that they simply don't have any more time to do moves (or don't have anything left off cooldown to do), and the resource system is basically only a limit to either a) longevity or b) (in the case of, for instance, DKs) which moves they're doing at any given time.

Rogues, on the other hand, have historically been different in that we're only doing moves about 1/3 of the time; we spend a fairly significant amount of time waiting for energy to do that next move. And what makes this interesting is the fact that time is not really a limiting resource; unlike other classes, we can manage our resources to create bursts of damage at particular times without reducing our overall DPS output. DKs are to some extent getting this ability in Cat, but outside of that (and obviously feral druids) we're somewhat unique in that respect - the fact that optimal play of a rogue is only partly about what moves you're doing - it's also about when you do those moves.

And this is what we're starting to be in danger of losing in Cat. With increased regen from haste plus Combat Potency and Vitality, it's not at all unreasonable that our regen may approach 20 energy per second, which means our maximum available pooling time - the largest amount of time we can allow to safely elapse between having enough energy to perform our next move and actually doing the move - is down to about 2 seconds. The notion of saving up for a burst of damage (or to improve the alignment of other timers - for instance, SnD/Rupture refreshes) is severely hampered because... well, because we just can't save for very long without capping out.

Hence, I'd like to see them do something to help restore this aspect of our play, which basically comes down to one of two things: either a) reduce our regen (the obvious solution to which would be to remove the not-terribly-interesting Vitality talent, though a nerf to Combat Potency might also work), or increase the size of the energy bar. It wouldn't even need to be by a lot - 120 instead of 100 would make a significant difference - but an adjustment of this sort would have significant benefits toward maintaining the playstyle of the class.

One could argue, of course, that Vigor is placed in the talent trees such that those rogues who need it can get it; the difficulty being that the benefits of a larger energy bar in PvE are largely stylistic/qualify of life, and to the extent that it is a raw DPS increase it's a circumstantial one at best - that is, Vigor is the very definition of a filler talent. And the problem is, the trees as currently constructed leave basically no room for filler in offspec trees (and no real room for filler at all in Assassination). Hence, Vigor as it stands really does not address the concern. If, however, the ability were made more accessible - for instance, by being converted wholly to a minor or medium glyph - that might also be a way of addressing the issue.