2 Points for anyone late reading this thread like me:
1) New games rarely stay above 60fps in all scenarios, especially faster action games with complicated character models (ie, unreal). They *average* high frame rates for benchmarks, but when the action really hits - which is when you really need the graphics horsepower - framerates can drop well below 60 (even on the best SLI rigs in SLI capable games). The argument that LCD users don't need powerful graphics because of the lower refresh rates is simply wrong. On the topic of LCD panels, response times <20ms are useless paper specifications that do not represent actual performance. I'm a pretty serious gamer (participating in competitive clans) and I switched late last year from a Sony 19" FD Trinitron to a Samsung 193P. I'll put my panel up against anything on the market for gaming, side by side. So far I haven't seen anything that outperforms it in the 19-20" range in any way (contrast, brightness, viewing angle, color reproduction, and yes even pixel response in actual gaming/video situations). My lame response time on paper is 20ms but I do have full 8-bit color.. but I assure you there are many 16ms and 12ms panels advertised on the market that present considerably more ghosting, streaking, and so forth in real application. I haven't compared to an 8ms panel, but I expect the results are the same (they are based on the same 6-bit panel technology that allows the 12 and 16 specs).
2) SLI did not save 3DFX, innovation from Nvidia in the form of newer technology allowed Nvidia to bankrupt 3DFX (which gave them ownership). They didn't break out this technology until they couldn't beat ATI in a single processor. For people who think it's cost effective in any way, consider how fast video cards lose value (more than 50% depreciation per year). Do you really want to have TWO components depreciating that rapidly?
If you can afford to buy the best every 4 months, then yes SLI is the current king. If you're one of the people that buys once per year, or even worse.. as the OP suggests, upgrading nothing but hard drives for 3 years... the SLI is a bad choice. Yes, it will rock for the next 12 months. Then it will be inferior to a single card solution in the second year. In the third year, it will be so far behind the curve that it's almost ridiculous that your actual cost is $1000 for the setup over 3 years.
A better solution for most people will be to buy an X800XL at <$300 now. Buy the same price range next year (at the beginning of the year). And buy a third in the third year. You get more than acceptable performance that matches up with your monitor, etc now, in all but the most taxing moments (during which even the SLI setup slows down), and you maintain that level of performance for all three years and end up spending the same amount of money (ignoring time value of money). I've been playing the 'top video card game' since the days of Voodoo SLI.. and it's a very expensive hobby.
Lately, the games pretty much blow in my opinion, so this year I'm running an X800XL until someone comes up with a game that keeps my interest for more than 30 days (please dear God leat Unreal 2006 be as much fun as Unreal Tournament was for 3 years).
And there's my $.02