Linkboost is a gimmick, I just read a pretty good article
http://techreport.com/reviews/2006q2/am ... dex.x?pg=1comparing the nForce 590 SLI and ATI's CrossFire Xpress 3200 chipsets.
It says that Linkboost only applies to the high end 7900GTX. Another thing I read says that the cards that would benefit Linkboost the most would be low end, and the low end cards aren't compatible. Mind you, the article is from May, so you may have newer info than I have. A 2% performance increase isn't all that swish.
I don't see either of these chipsets as a world beater, but they are ok. I particulary like the ATI 3200 chipset because it runs nice and cool, and it is pretty much a no frills chipset, while the NF590 is hot and complex.

Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24&