Compatibility is another claimed feature of Crossfire over SLI. The main problem with SLI is that if an application or game is not in the driver profiles, then Split Frame Rendering doesn't work as intended. The driver is unable to dynamically adjust the location of the bar and the screen is split into two even parts, each handled by a different card which causes a serious performance drop.
The NVidia Driver profiles
Although NVidia is working to keep the SLI-supported games list up to date, needing a driver update every time a new game is released or waiting for such a driver is annoying and one of the first things NVidia has to change in future platforms. At the time of the writing this article, Grand Theft Auto : San Andreas is still not supported, a month after the game's release.
On the other hand, ATI with its default rendering mode being Supertile, which statistically shares the load equally across the two cards without the need for load balancing, skips any kind of problems and is by default compatible with any 3D applications and games.
Another thing worth mentioning is that even though Crossfire products have still yet to come, the Catalyst drivers seem to already support them. We only have to wait for the first product samples to see how well they perform.