I just uploaded this alternate file to replace your filters.svg in your Inkscape filters folder : http://www.openclipart.org/detail/84109
Just backup the previous file and replace it with this one. It contains all previously existing filters + a bunch of new ones like posterizing, litho, funny painting, canvas bumps filters, etc.
Just some tips : inside filter settings in the Filters Editor, play with Blur and the different Saturation and Hue rotation Color matrices and you will obtain fast interesting changes.
Sorry, the filters tooltips and definitive names are not fixed at the moment but the filters work very well.
Have fun !