Thanks a lot Orteil.
I did briefly try Darktree and Mapzone, but at the time I had trouble getting my simple mind around them. Filter forge on the other hand seems a lot more intuitive.
Despite the lack of tutorials, the manual, although short, is very to the point and useful, and the vast resource of available filters to pick apart is staggering.
I'm really liking this program. The only problem I have now is that every time I come up with an idea for a filter, a quick search reveals that around six other people have already had the same idea