Dave Bradford had one of the same problems I deal with on a daily basis:
While using mobile Safari on the iPhone I sometimes come across a Twitter account I’d like to follow or check out, to follow them I have to select the users handle from the URL, open Tweetbot, go to search, then copy the username into the search field.
It’s a minor annoyance, but those few seconds you spend copying and pasting add up over time. Dave made a bookmarklet to open Twitter profile pages as usernames in Tweetbot – it works on OS X too if you remove “mobile.” from the bookmarklet to work with desktop Twitter pages.
Get the code here.
Update: Phillip Gruneich also has a few bookmarklets that look cleaner and work with both Twitter and App.net.