Author Existence Failure: GameSpy, which provided the online multiplayer for the PC version, ceased operations in 2013. You can still play LAN multiplayer, though.
Colbert Bump: Gave a little one to Cage the Elephant, the indie band who recorded the game's theme song.
Descended Creator: Crazy Earl the memorably mad merchant is voiced by Randy Pitchford, President of Gearbox.
Fan Nickname: The Secret Armory DLC is often called the "farmory" (affectionately and not), thanks to a glitch that allowed you to easily loot the many chests at the end with no time limit (whereas normal circumstances give you ~3 minutes to grab stuff).
Early trailers suggested a story-based, Real Is Brown FPS with RPG elements and Procedural Generation. It was changed to a colorful, Rule of Fun FPS/RPG with focus on More Dakka. There was an entire story that was mostly cut out and the art-style underwent a total overhaul unusually late in development. All the original concept art went unused, which actually led to one of the devs (the art director) leaving the game industry forever.
The fans and critics alike were disappointed by a lack of storytelling and the Final Boss being a Giant Space Flea from Nowhere, which most likely caused the developers to put a bit more emphasis on story in the sequel, though it still retains the run, shoot, and loot gameplay from the first game.
In the Game Informer article, they mentioned being able to disassemble guns into their parts so you could build your own super guns out of them. Not that it matters when you can find almost any combination you could want in game anyway (or build your own from component parts outside of the game with a gear construction kit).