If you've been on Twitter this morning, you've probably noticed that clicking a link redirects you to a "t.co" address that doesn't exist. Yup, Twitter links are completely borked.
The error was happening in Twitter's back-end this morning, and Digg pointed out, you can get around the problem by simply cutting and pasting the link into you browser.
Update: It appears that Twitter links are mostly working now. As The TechBlock points out, if you're still having problems with links, restarting your Twitter client should help.