Broken Links
Before events took this bad turn, the contract represented by a link was simple: “Here’s a string, send it off to a server and the server will figure out what it identifies and send you back a representation.” Now it’s along the lines of: “Here’s a string, save the hashbang, send the rest to the server, and rely on being able to run the code the server sends you to use the hashbang to generate the representation.”
Do I need to explain why this is less robust and flexible?
Mark Jaquith in the comments explains why Twitter is doing this and how hopefully it will stop being “necessary.”