Originally Posted by bob saget
The problem with SLi or with CrossfireX is that you don't double the performance with two cards, or triple the performance with three. I may be incorrect, and anyone correct me if I am wrong, but it is my understanding that every card you add "helps you out" less and less.
While you are right that scaling isn't 100% all of the time, it can and does get close to that in many games.
The biggest issue with SLI in my eyes is that it's still not as polished as a single card solution. There are still plenty of games that don't play nice with SLI, and there are even others that have bugs or other issues not present when you use just a single card.
After my 295 I swore I'd never do SLI again. That lasted about a week after I got my first 480. Now I have a much better opinion of SLI, but I still won't ever do "low end" SLI again, due to the aforementioned issues.