Resources produces an error when attempting to "Add Web Links (URL)" that are longer than 255 characters. 255 characters is an arbitrary limit for URLs. Internet Explorer accepts URLs up to 2083 characters, Firefox accepts URLs greater than 64k chars, Apache can serve URLs up to 4000 chars. More about URL length can be found here
http://www.boutell.com/newfaq/misc/urllength.html
We have had a couple of instructors report receiving the "name .... is too long" error when pasting in some ungainly dynamic URLs. I think a 2083 (IE) or 4000 (Apache) character limit would be reasonable in Sakai.