I have Crossfire 6950's unlocked into 6970's in my AMD FX system, I wouldn't say it's been problem free at all in regards to crossfire and I bought them at launch.
The 7000 series was also totally, completely utterly horrible at launch, if anything AMD should have delayed the 7000 series launch till the drivers were fixed.

As for the frame latency issues, it's not fixed, AMD have been going through games and merely making temporary fixes on a per-game basis, it's not perfect, the microstutter can also get out of control, it's pretty much the sole reason why I went Tri-fire on my main system not just for the boost in performance but to eliminate microstutter.

AMD probably will not get the frame latency issues fixed across-the-board untill they finish the re-write on the memory management system in the drivers.

Frame latency and microstutter can be perceived differently by different people, some people notice it badly, others don't notice it all, I'm in the former camp where I can notice it.
However, the main reason why I keep buying AMD stuff is because of the entire price/performance ratio, I can put up with the little niggles when I look at my bank account, but that doesn't mean I'm tied to either company, they just need to release the right card at the right price and I'm all over it.

I noticeed micro-studdering in some games when the framerate was under 40 FPS with my 6950's, but I think people need to know that Micro-studdering 30 FPS is still better than 20 FPS standard.  While the screen looks a little more slide-showy, the movements for me were never as jerky as it looked...

Ofcourse I was also crossfiring with one 6950 in a x1 slot so... lol!

you could try http://maldotex.blogspot.co.nz/2013/05/metro-last-light-sli.html

Or wait for Nvidia to fix their shit. Considering the games uses streaming for everything installing to an SSD should help if you aren't using one already.

I had some strange lighting glitches during my Metro playthrough though it ended up being that I overclocked my 4890 a bit further than normal. Really fun game even with my PC being brought to its knees during several outdoor sections.

I have to say, the first two Metro games have both been fantastic. 4A Games has come out with a great follow up to Metro 2033. As far as 'Metro' as a world goes, the setting, pacing, gunplay, and player engagement are on par with Half Life. Gritty post-apocalyptic settings have been done before, but never with so much attention to detail, and rarely  come together in something that ends up as a cohesive whole with few real failings.