In addition to building the binaries and running the tests (which when you take into account the publishing of the results to the project portal is actually WAY cooler than it sounds!) MS (Team) Build can also copy your binaries to a QA environment, which is how we use it.
The build runs nightly, the results are pushed to QA. The QA people check the portal in the morning to verify the new build is available and see what tests failed. Then they QA the new features and sign off (or not).
I don't know that I see Microsoft incorporating the building of MSI into Team, since it seems that Build is really geared to the type of situation I just described. When it comes to building MSI for distribution, I generally either want to do that myself or have one of my senior developers do that, and generally I only want that defined immediatly prior to release to make sure that is it fresh and refelcts the actual requirements of the finished product, and not what we thought they were six months ago.
Just my $0.02 :)