I wouldnt rag on SLI/Xfire too much.... although (IMO) undesirable from a power efficiency point of view [/tree hugger], the benchies are plentiful that at HD and UHD resolutions, which is what SLI/Xf really is targeted towards, that these setups outshine single card setups.
The fact that SLI/XF optimised mainboards and cards exist are testament to this. The manufacturers wouldnt make em if people didnt want them.
Another good example is the only setup where a testbed has gotten anywhere near decent HD performance in crysis is a TRI-SLI setup(see news thread). I dont think a single card is going to get near crysis at UHD/Maxxed for 18months at least. Maybe the 9800/9950(or AMD equivalent) in SLI will give it a good wallop - but not on its own at 1600p.
I would love to see what an optimised QUAD-SLI 8800Ultra setup will do to crysis, replete with decent QSLI drivers of course, though a small forest may need to be cleared to power such a rig
SLI is one of those love hate things, I think most people are wary of it because of the price factor, others the power consumption. Then you have those richer enthusiasts who occupy the other end of the spectrum