So recently I registered a few fun unicode domains. I think http://♹.com/ is my favorite that I registered. It took me awhile to figure out how to do it. I saw http://☃.net/ on iTod's twitter and it made me really want to figure out how to do it.
So the first thing to note is you don't actually register
xn--06h.com instead. This is also difficult because a lot registrars don't let you register xn-- domains because it is reserved. xn-- means that it is puny code encoded. Puny code is basically is a notation for encoding unicode characters into a more common character set.
So once I discovered that, all I had to do was pick a fun combination character, encode it into puny code, and then register it. The registrar that I used was Verio. Overall, I'm not a fan of them, but they were the only one that would let me register a xn-- domain.
So far, I've only seen Safari convert the xn-- in your address bar into the character or characters that it represents. It looks sweet in Safari, but everyone else will probably just be confused. It was a fun waste of an hour though.
Update: So Verio sucks. They messed up my order and never registered those domains I bought. Which is probably good. After I ordered them I was like, "Crap, I just spent $80." So it's all good.