I jailbroke my 4S last night, and haven't really encountered any issues (minus music being deleted), except for the grey backgrounds of all the folders and multitask bar.
It looks like the image was shrunk down to 1/4 the size. I've seen other people's issues with apps being shrunken to 1/4 of the screen, but this is centered in the middle and doesn't affect performance. I've been trying to attach a screencap but haven't been able to upload it on 2 computers.
I tried the solutions people used for the app shrinking (safe mode -> reset for instance), but this doesn't seem to go away. I also tried to force new background images through a top-layer theme (640x960), and while that did update the image, it was still scaled down, centered in the frame of the folder.
Does anyone have any other ideas? I know it would help with a picture... maybe it'll work later. Thanks in advance!