http://www.supercatjaguarspares.freeserve.co.uk
Host name comes to 40 characters, which should be just at Arachne's limit.
Protocol is 7 characters. I didn't try this with Arachne.
A few months ago, I posted a message about a long URL of 713 characters in an
about.com page. That included a lot of fluff, such as %255F instead of a simple
underline character_. I never managed to access that URL. The file and path
was well under 256 characters, but then there was a question mark followed by a
long string, probably some long-winded Web application.
