I've revamped the object specific preference system. This means that plugins can now easily add preferences specific to an individual contact (or all the contacts within a specific group). The contact alerts already had a system for this, but the support is now in Adium's core and easier to access :-)

I've added some temporary code to upgrade your preferences to the new system as they're read. Don't be alarmed if some contact-specific preferences are lost, however (aka. Aliases, Contact alerts, and custom voice settings). Sorry for the inconvenience.