Plugins/WordPress_Widgets for more info.
For me the widgets plugin did work out of the box in WPMU with no modifications to anything.
Currently I am starting to modify existing themes and adding this to them.
When I installed I treated this as a normal plugin, and put it in the plugins folder. I do want to put this in the mu-plugins so it is enabled sitewide, but I dont know how to modify the plugin. There were some instructions on the here on the board for converting a regular plugin to a mu plugin, but...
I do know of one problem
The problem is really weird - it won't drag & drop, and in Firefox, you can't even see the config button on each menu item.
Any ideas?