First of all SLI isn't a gimick.. two 660's or 660ti's out perform in games that support SLI by far. If your not a hardcore gamer then the 660 in sli will be perfect, mainly because if your game doesn't support it, it will just run off one of the cards assuming that the single card is powerful enough to play the game by itself (660 can play about 90% of the market by itself).
Secondly you should do some research to see if your games support SLI. Most mainstream titles support it like BF3, Crysis Series, Metro 2033, etc. If most of your games support it then go for it. If not then look into one higher end card. If your dead set on Nvidia the 660ti or 670 is a great place to go. For AMD you can't go wrong with the 7870 and up.
Third, instead of a gtx 680 look into an aftermarket gtx 670 (unless your going to waterblock it) like ASUS direct cu ii or MSI Twin Frozr. You can overclock them like crazy and at stock speeds the 670 is only about 10% slower than the 680. Plus it will save you 100 bucks that you can put to an awesome sound card or a better CPU, headset etc (I recommend the sound card).
Finally, it's not a gimick if it works. What commissar is calling a "gimick" is rediculous. If it was a gimick, then no games would work with sli. One of the whole ideas behind sli was to bring more performance by linking two cards while having the least amount of impact on the consumer cost wise.
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Opinion time:
My personal opinion for video cards is go for one solid powerfull GPU. I have finally upgraded from my 6870 and my 7970 is coming tomorrow. I originally was going to get a gtx 680 because I never had any problems with nvidia and with my 6870, my drivers would fail and recover in the middle of my games. The reason I got the 7970 instead was because they were giving 4 games at the time and because of the new drivers, the 7970 is actually faster in most tasks then the gtx 680, so I decided to give AMD another chance. Remember, it's no longer about who has the fastest chip but who has the better drivers.
Also if you end up getting one single powerful card now (660ti/670 or 7870), you can always add another one down the road if you want. Remember however the there is bound to be some glitches or bugs with any multi-gpu setup
No offense Commissar, but you start posting on things when you have no first hand experience with it at all. You have never used SLI or CFX before. It seriously makes a lot of us mad when you instead of helping you just bash on a idea or a technology, not because you had problems with it first hand, but because WHAT YOU READ about it doesn't appeal to you.