I had another look for torn paper tutorials and if you search for 'photoshop +torn paper' then there are plenty. They tend to fall into two catagories, drawing a ragged edge as a selection then applying filters or using brushes (and applying filters). The first requires a bit of artistry and the second has photoshop parameters not easily duplicated in Gimp.
Going for the second option, I played around with making some animated brushes which worked fairly well with the eraser tool, jagged but not exactly 'torn paper'
My solution, 'Occams Razor' - simple is best. Two large 'torn edge' brushes to use with the eraser tool. One vertical and one horizontal made from genuine torn paper which I scanned. Scale them up or down and nibble away at the edges. For an angled brush there is the brush-transform script, (much adapted by various people) If you hunt through the 'meet-the-gimp' forum, its there somewhere.
a sceen shot of what you might expect.
http://www.imageno.com/1uc6n874usripic.htmlIf you want to use the brushes I made & the brush-transform script they are on my rapidshare account.
http://rapidshare.com/files/413875241/torn_paper.zip.html (103 KB)
The brushes go in your local brush folder and the script in you local script folder.
Remember that the brush is not really a brush, it is a 'stamp' to be used with the eraser tool.