Volker Weber writes:

In case you have not taken the Groove tour, I would suggest that you do it now. You will be amazed by what you can do with the product. Less my what it tells you but how it is done.

You will also see the main obstacle. If you don't have Groove installed you can't take the tour. That is true for the whole product. If your coworkers don't have Groove, you cannot use it to collaborate. Big difference to other web-based collaboration tools like eRoom or Quickplace. How did Bob Balaban put it so nicely? A telphone does not make a lot of sense if nobody else has one.