- according to most reviewers, it's significantly louder under load than 280 GTX;
- it draws more power both idle and under load;
- it runs even hotter than the GeForce;
- it's still prone to old AFR issues like microstuttering, mouse lag, reliance on driver support, sudden FPS drops, etc.;
- it has its own issues like flickering in some games, BSODs, alt-tab errors, etc.;
- the 280 GTX runs pretty much all games smoothly in 19*12*4*16, except for Crysis, which the X2 can't handle either (in eye candy, VH), and STALKER Clear Sky, which is crap IMO anyway.
No. 1 (noise) seems to be true. I can't really compare, just ask apoppin. He has both cards, currently using X2. However, most reviews claim the X2 is louder by around 5 db under load, which is a lot (+2 db = roughly double noise). Its noise is not GF FX-like intrusive or annoying but it's there.
No. 2 and 3 are true for sure, that's just a fact no one can deny.
No. 4 is also true - it's still "good", old AFR so it still has uneven frame distribution and the like. However, this entire argument IS subjective to a certain extent and can be contested. Most users notice zero microstutter on the X2, and driver reliance doesn't seem so bad since in the worst case, you fall back to a single 4870-1GB level of performance, which is usually reasonably close to GTX 280. However, sudden FPS drops and lack of smooth feeling in terms of FPS have been reported by users in games like GRID, Bioshock, DIRT, and others. Seems random enough but a thing to consider.
No. 5 is something I can't verify by myself but it's based on user reports. Regarding GTX 280, you only find reports on overheating cards and some very rare issues. As for 4870X2, you can find a ton of posts on different forums concerning various problems with the card - from BSoDs during driver installation on Vista 64 to flickering issues or crashes in games. There are also users who claim there are NO problems whatsoever, but by definition, a dual GPU solution won't be as solid and stable as a single GPU one. I've also seen people return their X2s and switch to 280 GTX or another single GPU card, due to problems.
No. 6 is a mixed bag. In most games, the 280 is good enough for smooth eye candy gameplay in 19*12. In Crysis, it's IMO better than the X2 thanks to higher min fps and pretty much the same avg fps. In some games like GRID, it's stomped by the X2 but still delivers great gameplay experience in 19*12. STALKER CS, Call of Juarez or AoC favor the X2 and could herald a performance shift and 280 GTX running out of steam. However, (a) I don't think so because it really depends on engine, (b) none of the aforementioned games is worth playing IMHO (AoC = wasted potential), (c) by the time it happens, something new will hit the market anyway.