Mathematicians love to gossip. Now they have an outlet to do so online at the math jobs wiki .
All joking aside, I expect this site could be extremely useful for those people applying for jobs (especially tenure-track). In the fall, you can look at what schools are offering jobs and in the winter, as offers are made, there will be less guessing about which schools have or have not made their offers. Of course, it is too early to tell how many people will contribute and hence how good the information on this site will be.
One could argue that this type of service is harmful. Some people may feel that this amounts to an invasion of privacy and other may feel that it just adds to the frenzy and stress of job applications. Perhaps these people have a point. It will be interesting to see what the reaction from the mathematics community is. One should note that there is a corresponding physics rumour site which has been around for a few years and seems to be reasonably successful.