Borderlands 2 is a game that lives by its co-op - it's fun to play the game solo, but it's even more fun to play with friends. It's even more fun to play with a friend in the same room.
The PC version of the game is truly fantastic, with great graphics, snappy load-times, lots of tweakable options and a much-improved interface. But it doesn't allow for split-screen co-op -- if you want to play with friends, you'll have to do it online. Well, until now.
Over in the official Gearbox forums, user Sycdan has posted this thorough step-by-step guide to playing the PC version in split-screen. It involves installing sandboxie, IndieVolume (which costs money but which you can try for two weeks for free), and running the game in windowed mode. You'll also need two controllers that your PC recognises, naturally.
I haven't tried this, as I mostly live a sad and solitary video game life, but the whole thing looks viable, if a bit hacky. Given the way that Steam's big-picture mode has made PC gaming more of a living-room thing, it'd be great to see more and more PC games offering split-screen gaming right out of the box, just like their console brethren. Soon, I'm sure. Until then, where there's a will, there's a way.