I've used Photoshop since version 2.0, and since I'm a professional graphic designer and work for a prepress company, I know ALL about CMYK, LAB, spot color channels, etc., etc.
But when I go home to work on my own photographs, I don't need the vast majority of what's in Photoshop. Unless you're into "creative" special effects (blecch!) you'll be doing almost all your photographic work with just a few functions:
-- Levels (or Curves if you prefer)
-- Layers, layer masks, and layer effects
-- Healing brush, clone stamp, lasso, and Selection>Feather
-- Filters: Add Noise, Dust and Scratches, Unsharp Mask (although 'Smart Sharpen' in CS2 is even nicer.)
-- Image resizing and resampling in the Image Size dialog box.
(I may have forgotten one or two, but this is most of the basic toolbox.)
You can master all these with a few hours of concentrated practice, and they're really all you need to prepare and enhance unmanipulated photography.