The new default theme for new users is Blogging Pro by Elena G (See it here)
There are a number of different themes available for your blog straight away, some of them will require some attention from me as the site grows to add the ability for users to edit the options for displaying some of the custom parts of the themes.
If you’re a theme designer and you would like to add a theme to the list, let me know here or through the support tickets system in your dashboard and you could have your theme available to the 9000 or so users already registered on ComLuv. You can link to your site in the theme description and theme footer. I will get some guidelines up in the future for the best way to submit a theme and what options it should have to be compatible with WPMU.
Let me know if you’d like to see a particular theme available here