Thanks for the link. Will check it out...those are some cool textures.
FilterForge is a good program for making fills or textures (whichever your program calls them). It also can make them seamless, so that they tile well. If you have both FilterForge and ImageSynth, your possibilities in making files/textures are limited pretty much only by your own imagination. The Vintyri Project certainly values both programs.
if you're looking for tilling images, another to check out is PixPlant will tile in seconds from a photo and you can also correct something that's in perspective first. It also blends multiple textures,though probaly not as convinving as Image synth2 - I use PixPlant for 3D game textures really, so if you're not after normal maps and such then it may have stuff you wont use, but worth watching the "create seamless textures from photos" videos on their site just to see how cool the tech is.
Filter Forge looks good and is handy, going to get meself a copy once the trial runs out, but I would probably also use PS to work into what ever I produce as some of the results can look a bit flat and too procedual at times. Same with most PS filters I guess; the filter can only be the beginning or the end depending your vision and needs. The other thing I like is that it's got a resolution scale with it so all nice an sharp no matter what size your art.