Nirach:
SLI "cons":
1. Same cards, only same model (e.g. 7800GT) and that might not even be the case anymore. (I seem to remember they were working on that) Same model is maximum benefit anyway.
2. Costs a lot. There's no greater "bang for buck" upgrade, or even one that comes close. Also, Crossfire "costs a lot" as well. Performance costs.
3. Support. Please list 5 3d games that get no benefit from SLI? I think you'd have to visit nV's website to find a few games. IMO, SLI has as much support as most cards.