If you're just re-photographing negatives with a macro lens, for instance, you're probably not going to be extremely happy with the results.
Why is that?
A 20 megapixel DSLR camera with a high quality lens that can resolve at or close to that resolution is effectively a 4,000 true optical dpi scanner, that is not interpolating (more than 1 pixel or so) to get there, etc.
It also has reasonable dynamic range already, only very slightly below a typical 35mm negative for entry models, and at or above for nicer full frame models at 100 ISO.
Random 35mm neg I photographed a little while back (note that this is resized to be small enough to post. There is a little bit more detail originally. But you can still see individual threads in the in-focus dress):
Is it as good as a $1000 scanner? No. (edit: well, maybe if I practiced more, looking at that link light guru posted above)
Is it better than a $100-200 scanner? Yes.
Is it better than the photo lab down the street does while charging me 20 cents a scan? Yes.
But note that if you already have a macro lens or tubes and flash, it only costs about $5 for some glass to sandwich the negatives between. Also MUCH MUCH faster and less annoying than using a scanner, once you get it set up (click, slide glass, click, slide glass, click, lift glass, pull negative reel through to next 3, repeat, about 2-3 seconds per, and another 30 seconds per in photoshop actions, unstoring and combined time of storing the film, etc.). The convenience alone of usage is worth $200-500 dollars right there for a shoebox full of negatives.
If you want some negatives scanned well enough to make huge poster prints that will be viewed froma foot away, then pay a professional with awesome equipment to digitize those for you (or for the brave of heart, take a bunch of photos and photomerge). If you just want 4x6s or even 8x10s, and certainly if you just plan to share them online, photographing your negs is good enough.