Team System SP1 is due out...  sometime.  We still don't have a date from Microsoft (as of 10 Aug 2006), however, Brian Harry has provided us with a short list of some of the features to be released.  You can read about it here.

My favorite new feature is WIT Custom Controls.  This means we'll finally be able to host a control that will display custom data without having to rebuild the entire Work Item display framework.  Very cool.  A few already pop to mind:  a Grid display, graphical displays (small embedded charts), and maybe even a tiny Wiki.