Brian Harry has a post highlighting what's in the upcoming SP1 for TFS in Stuff in the pipe for Team Foundation Server. My favourite enhancement is excerpted below:
"WIT Custom Control support - This is a cool new feature. It is a mechanism by which people can design work item forms that host custom controls. The data behind the controls can either be persisted in WIT fields or elsewhere. I'm hoping people go crazy with it and build some awesome custom controls."
This was one feature I really, really missed in the RTM version.