Say I want to find all tweets that link to a particular blog post, such as this one, and considering that most tweets would actually use URL shorteners, is there a way to find those tweets, taking into account the tweet might contain the original URL or any of the shortened URLs?
I was looking for something similar for someone I know and I just came across BackTweets.
Here's an example searching tweets linking to webapps.stackexchange.com. When I ran that search just now, the oldest result was from two weeks ago. Twitter's own search only went back five days for the same query. BackTweets also found results that that Twitter didn't; perhaps because Twitter doesn't unwrap as many shortened URL types?
BackTweet's free service has a tweet history for URL searches of between 2 – 4 weeks, and the pro service ($100/month, ouch!) advertises 2 years tweet history. If there's a strong business case, perhaps that's worth it.
** UPDATE 06-Jul-2011: BackTweets (BackType) has just been acquired by Twitter. **
(p.s. Even though nobody had upvoted my answer, <sniff>, clearly Twitter saw value in the service ;-)
All that Twitter will have will be the shortened URL, so you will have to run the URL through the most likely shorteners yourself and search for their output.
You'll also have to search for the full URL as well, just in case someone posted that.
Twitter Search will search "within" a shortened URL (at least bit.ly powered ones...)