SLi = Nvidia monopoly.
On AMD platform, the option to go SLi isn't all that bad, as Socket A, 754, 939 and AM2 were best when paired with their respective nVidia chipsets.
On Intel though, 680i was just jack of all trades, master of none apart from SLi. Slower clock for clock than most Intel chipsets, slower RAID, unlinked memory was a good point but left massive FSB holes in some configurations.
I bet if Intel made an AMD chipset it would be the better one.
I do miss the stability and simplicity of my NF4 + 939 Opty setup though, I very much doubt that RD790 from AMD will be that amazing. RD420, RD580, RD600 were nothing special and beaten by the nVidia chipsets.