Random theme on signup. Does not seem to be working.

I have 3 avaialble themes (woothemes) to select from (see attchment) and when a new signup occurs it always uses the twentyten theme. Seems this plugin has no effect. I unzipped plugin uploaded the random-theme folder to wp-content/plugins folder. I went to plugins and clicked "network activate". I am using WP 3.0.4.

Anything I have forgotten?