I haven't actually used any GEGL filters, this was a botched HDR converted to greyscale. I only recently appreciated the potential of greyscale images, after reading an article on using the channel mixer to manipulate the look of a mono conversion. I find ufraw very good for this, although I normally use rawtherapee on raw files.
I think people would use GEGL a lot more if they moved it from tools to filters. I personally haven't had much luck with raw converters other than UFRaw.
I'm in the same boat. When I first bought my camera Rawtherapee was the only open source program that I could find that supported my camera, since then UFraw has added support, I like the GUI of UFraw but rawtherapee I find has more options (generally speaking).
I use CHDK with a Canon that does not support raw files from the factory, so not all programs support these files. It's understandable, but what I don't get is why even after I convert them to DNG they still won't be read. RawTherapee does work with my files but white balance and noise is a major problem.
Does CHDK give you the standard canon raw format or is it different? I remember seeing on the ubuntu forums a few people have trouble with canon's raw format, I was surprised because canon are a major player in camera's. It is strange that the DNGs aren't read.