I believe in last months PAD thread Pierre asked about how I shot the panorama below at the focal length that I chose of 14mm.
So, first, sorry to Pierre for not replying more promptly. And second, here is a pic that shows you what another 14mm stitched pano looks like before any cropping has been done(16-20 image stitch, I think).
As you can see, the only real distortion thats suffered is forced to the perimeter in much the same way it does with a single frame. The beauty of the vertical stitching is that when you make the image large enough you can trim away all or most of the distorted frame and still be left with an image many times larger than a single FX frame. The thing to remember is to shoot a lot of overlap so that the software has the most amount of useful data to work with. It makes for longer processing times, but the results are worth however it long it might take you.
The cropping above is arbitrary for the sake of demonstration, but the great thing about starting with a large image is that its often not too difficult to crop farther down and even out of the frame and then use content aware software to fill or simply clone it in manually if its too tricky otherwise. Meaning that if the distortion is tolerable, and it quite often is with the 14-24, you can crop very little away with excellent results. Surprisingly, a lot of my final cropping dimensions are very close or exactly the same pixel dimension as a single frame would be, except that its taken mostly or completely from the lens' sweet spot and thus gives you a very different image than if you simply took a similar single framing at 14mm.