Eric Lee has updated is Hemi tool to RTM version of Team System.
This tool, allows you to move work items across projects.
It also allows to move a given workitem to a different workitem type. (ex task to bug), the fields that can be mapped will be mapped, the ones that don't make sense are sillently dropped.
Probably moving from task to bug, doesn't make much sense, but will be usefull in a scenario where you want to move work items across projects that use different process templates. (eg from CMMI to MSF Agile).
It also has other useful features, like checking for missing values (again moving from items from projects that use different project templates).
You can read a more thourohgh description here (and obviously download the tool :-))