I have a question about WP MU is it possible to make users to use only one template and to block some other features like upload themes, plug ins etc? Thank you
I use MU with Buddypress and yes all of that and more is possible. First of all concerning the the themes, if you go to Site Admin->Themes, you can allow or disallow which themes are available site wide for your users. You can also assign certain themes to certain blogs by going to Site Admin->Blogs and choosing the "Edit" button under each individual blog. There you can set specific permissions for each blog including the theme. Plug ins are the same way, you can choose to activate them just for the main site, or on the far right there is an option to "Activate Site Wide". Plug ins installed in your MU Plugins folder are automatically site wide functions, but generally for Admin stuff. Your users should not have access to do anything with plug ins, actually you have to allow the plug in menu to be seen by all. IF you want to block certain themes and certain plug ins from certain users, and have them available to others, then you need the "Supporter"plug in and the only place that has it is http://premium.wpmudev.org/..it's a membership deal, but it is completely worth it if you are going to be working with MU. They have all of the cool plug ins and they actually work ! with support. Trying to find free plug ins for MU is a pain in the ass and most aren't even up to date.