Not precisely sure how bugs get reported in WordPress (I'm new to running a WPMU server), so I'll report one here.
I'm using WordPress MU 1.3, freshly installed, configured to support subdirectories. On the "home" site, I am using the xMark theme ( http://blogdesignsolutions.com/ ). Curious to try it out, I installed the "WordPress Mobile Edition" from Alex King's site at:
http://alexking.org/projects/wordpress
The plugin installed fine into the plugins directory (not mu-plugins). It activated fine for the main blog. Everything looked good.
However, when I went to my Blackberry 8830 and then tested the site by going into the Blackberry web browser and entering the site URL... the theme reset to the WordPress mu Default 1.6 theme.
After I reset it to the xMark theme, any visit to the site by the Blackberry browser would again reset the theme to the WordPress mu Default. To rule out that it was an xMark issue, I tried applying other themes and had the identical result. As soon as a Blackberry visit hit the site, it reset to the default.
In case it was an issue with the main home site, I also activated the plugin for a blog on the server that used the Tarski theme. I entered that URL (with a subdirectory) into the Blackberry browser and once again the site was reset to the default theme.
I do not have any other mobile devices with a web browser to test from (and the site is currently in development so I can't point to it).
Obviously I'm deactivating (and in fact removing) the plugin for the moment. I will also send Alex King an email pointing to this forum post. I just thought I would post so that others might be aware of the issue.