http://img837.imageshack.us/img837/562/15315978.jpg

I was just messing about (I'm fairly new to Inkscape), but got this cool effect (it was just one simple action) on this picture (the above shows several variations of it, using different settings). I just can't re-find it now. Could somebody help me out?

Do you remember if it was a filter?
You could get that effect using Path menu > Trace Bitmap. But it's not a filter. And I'm not sure what kind of filter it might have been. Maybe someone else will have an idea?

You could try to replace your filters.svg file in your Inkscape filters folder with this one I just uploaded on OpenClipart. It contains a bunch of posterizing and litho filters.

http://www.openclipart.org/detail/84109

ivan