Within my child theme I have code which creates virtual blogs within a single blog. Each virtual blog can have it's own Site Title, Site Description and stylesheet. I'm removing the code for separate menus and will rely on the new WP3.0 menu system in conjuction with Widgetlogic. It doesn't separate posts in the database or anything fancy - it's just something fairly simple.
Structurally it belongs in a plugin rather than within the theme so I'll be migrating it to a plugin. I could generalise it and release it generally, so I thought I'd ask whether there is any interest in a virtual blog plugin now we have wp3.0 networks. I'll continue to use it myself because I find it easier to manage virtual blogs within a site than a network - and of course I can combine both.
Theoretically it could be generalised and work with any theme but I am so used to Hybird I find it easier to write just for Hybrid and I've no need for anything that works on other themes.