I also have 20+ invites if anyone wants any.
Like everyone else, I have not found a use for this yet. I used it on a project with a team creating a business plan, but it was used exactly like email would have been, so it provided no benefit (and it's worse than email since the attachments and messages are not downloaded to your machine for off-site viewing). I already have to check email, IM (MSN, ICQ, Y!), Skype, and forums, and now they want me to check yet another thing? Nope, not for me. No compelling reason to use it yet.