If you try to enter a internationalized domain name as your "website" in your profile, it will be silently stripped of any non-English characters.
Ex: My webiste is http://linus.unnebäck.se/ but when I try to enter that it saves it as http://linus.unnebck.se/
when it actually should display linus.unnebäck.se
and link to http://linus.xn--unnebck-9wa.se/
(or just link with the ä, don't now what is the right thing to do).
As I wrote this post I also noticed that the markup ends the link at the first non-English character aswell, look at the example above.
markup
I mean the form where you write your posts, or actually the backend which converts the things I type to (x)html.