PC Perspective posted a review on the performance of 3-Way SLI running today on an nForce 680i SL motherboard.

NVIDIA has just taken its performance lead in the world of high-end consumer graphics and trumped it by introducing 3-Way SLI to the world. Though we have some minor issues with what cards NVIDIA has setup for 3-Way SLI compatibility the fact is that the performance results from our testing are freaking incredible. There are definitely some major games that need to be addressed in future, Crysis being the most prominent, but our initial impressions proved quite pleasing.

NVIDIA 3-Way SLI Technology Review - 8880 Ultra x 3