Don't know about circulated coins, but with proof coins there are many listed on eBay as double dies that aren't as severe as the fine example in a previous posters avatar (heh, heh, heh). I would guess that one that is blatantly blurry would be worth more than one with just a little doubling visible, but they sell for a premium on ebay.
I've seen proof nickels that usually sell for 2 or 3 dollars, sell for 4 or 5 when they are listed as double dies.
I've been straining my eyes checking out my proof sets.
On a side note, found a guy that had 6 silver 1992 proof sets listed as run of the mill 1992 proof sets. Got all 6 and shipped for around 42 dollars. silvah!