Icon themes provide icons for all the different types of file. The current series of ROX-Filer (2.2.x) supports freedesktop.org icon themes; install new icon themes in your ~/.icons directory, and then select it in your Options dialog's 'Types' panel.
Themes are listed in the Themes block on the left of the page, or you can browse the list of themes.
In The Future, we hope to be able to share icon themes with other desktops.
The filer uses GTK to load images. As long as you have SVG support in GTK, ROX-Filer will load them fine. To test for SVG support execute:
gdk-pixbuf-query-loaders | grep svg
If you get a line with svg_loader.so in it, you should be ok.
Make sure you don't have any Choices/MIME-icons directories (~/Choices, /usr/local/share/Choices, /usr/share/Choices, etc). These override icons set in the theme.
If you've previously installed ROX-Filer 2.0.0, you probably have one of these directories around.
"What's the best/easiest way of creating icons sets for using in ROX-Filer so that they can be shared ?
Do I have to manually drop an icon in the box for every MIME type, or is there some App that does this is a smarter way? I would like to make a bunch of icon sets and put them online for download."
Copy the ROX-Filer/ROX theme directory as ~/.icons/MyTheme and edit the icons there. Use the Options box to select your new theme. Delete/move everything in your Choices/MIME-Icons directories or they will override the theme.