Some of the user agent strings I've seen have bordered on being spam but this one takes the cake:
18.104.22.168 - - [15/Jun/2005:00:05:27 -0400] "GET / HTTP/1.1" 200 49441 "-" "The biggest cloud of domain name registrars, domain name registration prices, domain name classifications, domain name select suggestions, domain name on sale information, and the in depth analysis of domain names! http://sitesearchbydomain.com libwww-perl/5.65"
Despite the name, the site doesn't have a search option, but only provides a list of domain registrars.
It's registered and hosted with Schlund + Partner (part of the huge German "United Internet" conglomerate) and owned by a Xijie Yu in Atlanta.
I see we received a bunch of those spams back on June 8. If we get more of those, I'm going to test what Schlund's abuse department (which is a bit slow sometimes, but working) thinks of these ...
In the meantime, I'm left wondering what the point of the exercise is. There don't appear to be any affiliate IDs on that site and no ads either.