Even though I use to love Ambush, I have to say it's probably the most pointless ability in my ******* right now (except perhaps feint). We've talked about it before; the pretty number rule only works when you're specced for it, I think. At the moment my eviscerate crits top my ambush crits by at least 2000 damage.
When somebody says it scales terribly, I'd go as far as to say that's an understatement. I'm actually starting to wonder if it scales at all, as horrible as the ability now is.