I have read several places that putting the plugins into the MU-Plugins directory activates them site wide. That you shouldn't put them all in that directory, and one should be careful which ones go in. So far all of the premium plugins have been for the MU-Plugins directory and a few free download ones too
First, I was surprised that there were no pre-installed plugins with the default WPMU install. It could be only in the two themes that I've looked at. I will activate all the themes and then take a look at them all.
-Are there no preinstalled plugins?
-Are most of premium plugins for the other directory, "Plugins" or for "MU-Plugins"?
Any other words of wisdom for a new WPMU site owner?