I'm currently stuck on version 2.71 no matter what I do to try to upgrade. Each time I try only the first blog is seen and everything else cannot be redirected properly and generates 404 errors on the front and and the back end admin stays on the default blog and can't get to the others. We'll figure it out eventually but...
This led me to wonder how safe it is to continue with WPMU as things move along. Right now nothing I can do will upgrade beyond this point and already I'm seeing themes that won't work with 2.71. I'm wondering whether there is a fragility of potentially losing links to your blogs should you put your site in the hands of admins who might not be aware of the finer areas of how WP works.
Now if this was a WP blog for each one, we wouldn't have to worry about all this stuff. My goal was originally to have 3 blogs with just one login/identity for each of our users so their writing could appear in what seemed to be three different blogs on one site, e.g. /cars and /bikes and /trucks.