First of all, great plugin.
I am using this on a normal 2.8.4 wordpress installation with no issues what so ever. Some people suggested they had problems when they had more than one RT widget in a sidebar and I have not had this problem at all.
I am however, having a problem with WordPress MU.
The widget activates and lets me insert it in the sidebar. The problem is when I "save" my content.
For some reason all the apostrophes and what not get escaped.
Example: I insert an image and save. The image then turns into:
<img class="\"aligncenter" size-full="" wp-image-25\="" src="%5C%22http://domain.com/files/2009/09/copcar.jpg%5C%22" alt="\"copcar\"" height="\"98\"" width="\"193\"">
This is my first time really using WordPress MU, so I'm guessing this is something WPMU specific.
My next option is to go under the hood of the plugin and look around, but since I'm not familiar with WPMU I was hoping someone would have some insight first.