Just a note that there is a bug in the code we're on which causes problems using the 'theme selector' (pull-down menu on left) to set your default theme. If you choose a theme using the theme selector and leave the site, when you come back the theme will be defaulted to the site default.
To work around this, for the immediate future, you can login and select PROFILE (user CP), then Look & Layout Preferences. From there, change the theme to the few that are loaded there. This will stick.
If you are using Mozilla, it will function properly...
Sorry for the inconvenience.