You can do vignetting correction using RawTherappee:
Love the SX40SH + chdk DNG.
Some nice pano examples here:http://www.flickr.com/photos/mikedie1/
Nice bokeh:Danbo on the edge
David, you can also try an lcp profile to use with RawTherapee and others:
To remove vignetting is preferable to use flat frames
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