SLI does incur some overheads and some of the following games illustrate a few potential pitfalls with SLI.

Splinter Cell

The original game in the series is CPU bound for the most part. At 1024, the processor overhead of SLI negates any benefit SLI has in the video department but that slowly changes as the resolution increases.

Half-Life 2

Half-Life 2 has similar characteristics as Splinter Cell being heavily CPU bound. Differences start to become more apparently with AA and AF turned on above 1280.

Call of Duty

Jedi Knight 2

UT2k4

Jedi Knight 2, Call of Duty and UT2k4 are a few games that SLI does not really offer any sort of advantage in. Being very processor bound all three games take a big hit with SLI enabled when compared to the single card solution. NVIDIA should probably address a way to toggle off SLI support dynamically for certain games with the Forceware game profiles rather than forcing a reboot.