I suppose it's all a matter of how you use the tool.
For example, I used to always use Levels exclusively, thinking it was the same thing as Curves, only easier (easier for me to wrap my head around). But they are definitely different animals. And the latest Photoshop (CS3) makes that point all the more obvious by including Levels and Curves functionality within the Curves dialog!
I can't speak to using exposure / gamma / offset so much other than to say that exposure will change the overall brightness of the image (every value in the image is shifted up or down) and gamma will adjust the contrast of the image.
Levels, on the other hand, lets you determine where your black point and white points are. In doing so, you are also adjusting contrast by compressing your tonal range. But it's like a bull in a china shop, you have very little control over how it compresses the range, other than to see the two limits and then play with the middle slider (essentially the gamma of the image).
Curves, however, lets you "finesse" the tonal range of your image. Usually the adjustments are very small and the shape of the curve is only slightly off of a straight line! But the effect is profound. You not only get to adjust contrast, but you can determine what parts of the image are boosted in tonality and which parts are suppressed.
With CS3 in the Curves dialog box, you can do both at the same time. Set your white and black points and THEN apply curves all in one step.
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