I'm just beginning to look for post-processing SW,
Lightroom seems to be the most-recommended so far. Does Gimp accept RAW files, will it auto-correct lens distortions, and can it correct CA?
I've used GIMP, CaptureNX, Photoshop, Bibble (now defunct), and Lightroom. Each has its strengths and weaknesses but IMHO Lightroom is the best-of-breed for a
photographer's needs. Lightroom's strength is its workflow capability. Importing, viewing, rating, processing, cataloging, printing, and publishing are ALL done (and done VERY well) from a single interface.
Keep in mind that GIMP is just an open-source attempt to recreate the main features in Photoshop (now CS). I've seen many folks poo-poo Lightroom when compared to CS (and by extention, GIMP). To me they are two different types of software. CS is hands-down the best software for
graphic design. But it's much more power (and a higher cost) than most photographers really need. It's not unlike driving a Ferrari to McDonalds (no offense to McDonald's fans). Most photographers don't usually need the ability to add/edit layers, burn, blur, morph, etc. Lightroom, on the other hand, was designed specifically with a photographer's needs in mind. As I said above, it handles everything we would do in the normal course of processing an image.