Hi Marcus,
I have been in the beta program since October and can tell you this: Most of
the time nobody e-mails you an invitation to download the newest release.
You have to go to the site and see if it is available, or be in touch with
people in the community who will tip you off.
Beta testing is a pro-active activity; that is you cannot expect to sit back
and have anything handed to you. If you are on the true beta program
(Microsoft Connections) then there is a website with every download since the
first release available, as well as forums, announcements, and much more. If
you are on the public beta it will be more confined and you will not have all
of the releases and fixes readily available, but you still have to pay
attention.
Good luck!
M