Pros: Ample 2GB Vram allocation, Crossfire scales 90% on average, High overclocking headroom, Crazy cheap upgrade solution; Epic Price/Performance
Cons: 100w TDP; Gets hot under full load, Outdated and underpowered compared to the newer 7970M
It's based on the Barts Pro GPU, the 6850, and only mildly underclocked by comparison to it's desktop counterpart. The GPU itself features the full specs of the 6850, minus the core clock (680-MHz vs 775-MHz) but other than that the GPU is phenomenal. Often times, I can game harder and better than the 6850 due to the 2GB Vram allocation.
I've currently got mine at 650/900 @ 1.0v versus the stock settings of 680/900 @ 1.1v. The lower voltage and minor underclock both help with power consumption and heat issues that the card may present to you. There's no performance loss and the card runs crazy cool after the undervolt. I get a solid 10-15*C difference after the undervolt. It overclocks more than well enough too. I got mine up to 825/900 and scored over 14k in Vantage.
As for games, I can run Crysis 2 in DX11 with most settings on Very High with 60 FPS, dips into 30 FPS when a graphic intense cutscene rolls through. At the moment it's exactly on par with a GTX 465 and I couldn't be happier with the performance. If you look at the FPS you get with the 465, that's what I get with this thing, except with better tessellation.
The main cons at the moment are few and yet fairly problematic. The 6990M can be had for not much more, roughly $50 more on average between used parts or up to $75 between new parts, the 580M goes for around $100 more and more than just outperforms it, and the new 7970M is literally as powerful as two 6970Ms in Crossfire AND can be had for roughly the same price as two of this GPU. So all in all, it's got it's drawbacks there. The 100w TDP is the big one here as all the other listed GPUs here are ALSO 100w TDP and the 6990M is roughly 15-20% faster in every scenario.
The other big problem is that the GPU by default is already overvolted for stability and thus generates a large amount of unneeded heat. This tends to be the biggest turn off for most users since they want their laptop to be at least moderately cool in a figurative sense. I hit 85*C in most DX11 games, and that's with a cooling pad.
Aside from those two issues, it's a phenomenal GPU. roughly 50% more powerful than the Mobility 5870 and easily the best bang for buck at the moment. If it matters, it's more powerful than the 570M/670M too.