While this article mostly comes across as being written by someone who hasn't actually RTFM of the major calendaring software packages, it WOULD be great to hav

While this article mostly comes across as being written by someone who hasn't actually RTFM of the major calendaring software packages, it WOULD be great to have some sort of real-time peer-to-peer free-busy system that could interoperate across calendaring systems. Of course, you'd have to have a pretty robust permissions system to make sure that you couldn't just look up anyone's availability, but I think that's a solvable problem if users could exchange permissions when they schedule their first meeting together. For most of corporate America, shared calendaring is probably the #1 feature keeping them tied to Exchange Server. Solve this problem elegantly, and you could kick Exchange to the curb.