We're selling a lot of IDN's these days so from our perspective it seems a growth area. As far as SEO goes, I noticed a few pop up in the SERPs for competitive (poker) keywords the other day but they seem to have gone down again.
It would be interesting to run some tests on them, as I'm still not sure the punycode version of the keyword gets counted. For example here (покер = poker)
PHP Code:
<a href="http://www.xn--e1ajldi.net" title="link title" rel="nofollow">link text</a>
Do the SE's translate xn--e1ajldi into 'покер' when ranking the link or is it just transformed in the browser/SERPs as a visual thing.
So far most people seem to be buying them for type-in traffic or branding, I don't think many SEO's have got into them for ranking but it does make sense to have the domain keyword as a high ranking phrase. Plus there are still a lot of good keyword domains available.