Here's a completely different way of doing tags:

First, standardise sets. We probably want to go with a format along the
lines of:

    eapi = 4
    description = Monkeys

    dev-monkey/howler
    dev-monkey/spider
    >=dev-monkey/spanky-2.0
    dev-monkey/squirrel

where eapi has to be on the first line.

Second, make a bunch of sets named kde-tag, editors-tag, xml-tag,
monkeys-tag etc.

Third, make tools that allow browsing, searching etc able to list
things by tag (or sets in general).

Advantages: dead easy to implement, backwards compatible, we need sets
anyway.

Disadvantages: doesn't use some horribly convoluted system of XML,
wikis and web 2.0.

-- 
Ciaran McCreesh