We tend not to make judgements about hardware we do not have.
You should keep in mind that in case of professional applications (e.g., workstations) NVIDIA Quadro products will be used along with appropriate drivers (with its own optimisations) and software.

You mean like the 'optimizations' NVIDIA used to cripple nForce4 Ultra and try to squeeze $20 more for the SLI chips? NVIDIA has been using the uniform driver model for a long time, so any improvements made for the professional line is bundled in the same drivers as the regular products. Besides, it isn't first time the company trying to sell 'higher grade' product that costs nothing extra to produce.

Here are some quotes from the article with some additions:

1. "NVIDIA’s innovation also proved to be most fastidious about the installed cards – only two identical cards from the same manufacturer would work together. We couldn’t make two GeForce 6600 GT from different makers work in the SLI mode, despite their having identical characteristics and the necessary connector." Graphics cards evolve after time, particularly, BIOS versions may evolve.

2. "The problem is that besides the synchronization overhead and the lack of support of some games, the amount of graphics memory of two GeForce 6600 GT cards will remain 128MB, rather than 256MB, since the cards in the SLI mode have identical memory contents. This memory size isn’t appropriate for a high-performance solution intended for high resolutions and full-screen antialiasing..."

3. A year after you will be able to get a new mainstream board for $200 that has 2x performance of the GeForce 6600 GT and new features.

Thanks, I thought of these things, but just couldn't put together :) So if I buy a budget system, there is no point in SLI. I think I'll wait for AMR to show up, maybe it could be more reasonable in terms of price and performance.