Pretty neat, at first I was thinking you were talking about custom vhosts.
Also
>dat join rate ( for 2 minutes after global ).
Dec 22: [ Rizon.Xmas.Event.2010.Jan ]
Dec 23: [ Xmas.at.Rizon.Jan ]
Also note, using \ or _ in your nick will not allow the vhost to be set.
And another note: autoop ( on nickserv ) needs to be on for this to work as well ( this is on by default, if you have set it to off, change it back with /ns set autoop on ).