Ive Got a Geforce 7950 GX-2 which is basically 2 Cards in one Port SLI'ed
And frankly , its not that much on an improvement at the moment there are no games that Truly support SLI there are a few coming out , Like Supreme Commander, but that wont USE sli , it will actually Use each GFX card separately to give you 2 displays..
I expect that the games that come out later this year will have better SLI results