Seems like the general thought here is that they're almost always a scam or overpriced.
My two cents: I have gotten a few rolls of pennies in pasts months out of curiosity (and fully accepting the likelyhood of a total loss). Some rolls are complete wastes (nothing but circulated terrible 50's), while others I have pulled beautiful uncirculated early wheat dates(1910-30) or indian heads out of. I guess it is just luck of the draw, similar to getting a box from the banks. Haven't found any key dates in ebay rolls, although to be fair I wouldn't expect to find them in bank rolls very often either. I'd say most of my best pennies (visually) are from ebay/amazon rolls. Now, whether they were worth the price I paid... couldn't even guess. I have no experience in grading/valuing coins of any denomination.
That said though, I wouldn't be prepared to guess at what my ratio of "success::failure" might be. I'd imagine it probably doesn't look great.
FormerTeller: I had actually never heard 'caveat emptor" before. Made for some interesting reading when I looked it up, thank you.