I learned an interesting lesson about URLs and social software; change your article’s URL or publish it under multiple cases, even with 301 redirects, and you’ll end up with fragmented references.
Back in August 2005 I published the article “Well Designed URLs are Beautiful“ on my personal blog and have since had well over 400 people tag it on del.icio.us. Unfortunately during that same time, I’d changed my blog configuration twice to improve its URLs with one more change planned. Of course for each change I made sure the old URLs were redirected with a 301. Unfortunately, these chances resulted in my article being tagged from three different URLs, and hence splitting up it’s ranking on del.icio.us three ways!
So, when changing URLs, be careful. You could harm yourself in the process.
P.S. As an aside, this speaks sadly to ones ability to reorganize a poorly organized website, notwithstanding the fact that Cool URIs (aren’t supposed to) change. I can understand why del.icio.us and others don’t automatically test their links for 301s on an ongoing basis because of the resources required, but delicious and others could offer a “check me” test for links. This would even give them a legitimate reason to periodically email their users and say “Hey, here are all the links that moved!” That email could even ask “Should we keep the changes?” to guard against spammers, though I don’t think this would be a big issue. It is hard enough to get delicious links, how would spammers get them to begin with?
Anyway, I hope to see things evolve in the future where changing links won’t be such a big issue. And yes, sometime in the reasonably near future I plan to be an advocate for some specific plans to enable this.