user on NeoGAF who goes by the name Durante managed to unlock the resolution potential on PC.
Here's the original thread - http://www.neogaf.com/forum/showthread.php?t=488088&page=14
He's still working on some things, I will update the OP when the complete fix is released. This man deserves a paycheck from From Software, seeing how this will boost some sales for sure.
Here it is - http://www.neogaf.com/forum/showthread.php?t=488240
LATEST VERSION OF THE FIX CAN ALWAYS BE FOUND HERE - http://blog.metaclassofnil.com/?tag=dsfix
What is it?
It's an interception d3d9.dll that you place in the same folder as the game executable. It intercepts the game's calls to the DirectX 9 API and changes them as necessary to enable a higher internal rendering resolution.
How do I use it?
Place d3d9.dll and DSfix.ini into the game's binary directory. (The place where DARKSOULS.exe is)
You can open DSfix.ini with a text editor to adjust the desired internal resolution.
Will it work?
So far, this has only been tested on my computer, on the first half hour or so of the game. I can not and will not guarantee that it will work for anyone else, or not have any adverse effect on your game/computer. Use at your own risk! If you encounter any issues that seem like they could be caused by DSfix, let me know.
Will it cause performance problems?
That depends on your system configuration. Usually, performance scales rather linearly with framebuffer size, and so far this game does not seem different. My 660 maintained a locked 30 FPS throughout ~ 1/2 hour of testing in the starting area of the game at 2560x1440.
Can I donate?
If you really want to donate I won't say no, I'm not particularly rich :P.
Here's the link.
Also, a delicious new screenshot.
Also, a comparison screenshot.