I'd be surprised if they use the X for anything other than simple hiding. This was a feature I was pretty interested in about two years ago. I spent some time

I'd be surprised if they use the X for anything other than simple hiding. This was a feature I was pretty interested in about two years ago. I spent some time trying to use the pre-Application-Platform API to build it out myself, but there were too many limitations on the FQL querying API. At the (relatively small) Facebook developer party at SXSW in 2007 I talked with one of the Facebook employees about wanting this feature, and he said they had it working internally, but that they faced similar problems with the user experience; for instance, they would get all of the people they know well but hate. I imagine that they held back from releasing it until they came up with the "X" dismissal feature so that users wouldn't have to be continually annoyed by their enemies.