From the Photo it appears to only be the lip, the lip that stops the belt from jumping off - should be fine. It's on the inner lip too - you'd have to be really really really unlucky for this to cause a problem I recon - I'd reuse it if cash was an issue......
(It'll Probably last way past when you have cash to do it, I've seen some pretty scabby pullies running for years!)

Be thankful it wasn't actually the bit with the timing marker...! (That would be just typical!)

If you re-use this it may create a slight tapping noise if the belt touches it (For a while) but run a file over just the inside of the lip should work - don't cut the damage out just make sure nothing is pertruding in a direction that it shouldn't be.

Final note (As we always should) - check often, if it starts to look bad catch it before it may become a problem, knowing there is a problem and how serious the problem is, is the first step to saving big cash!

And guys calm down there's going to be a fight the way you lot are carrying on - these are all just opinions....

(P.S. I think that they are tyre tread patterns! <img src="/forums/images/graemlins/cheers.gif" alt="" />)