I want to give some more feedback now that it has been a few weeks.
I have had both raisin carbed beer and the corn sugar primed beer side by side and have not found much different.
What I have found different is the raisins carbed the beer more than the measured sugar did. We primed half the batch to 2.2 Vols and we used 3 raisins in each bottle for the other half. The raisin batch seems to have a little more carbonation.
I still can not confirm any sort of flavor from the raisins. I feel like there is a very, very slight difference between the two, but I am unsure if its because I know they are different. I think I will have to do a blind tasting with a few people and see if they can find a difference.
I will say that the carbonating with the raisins has leveled off. I know there were some people that thought the raisins would add some wild yeast, but I do not think this will be the case. Maybe we got lucky (we did not sanitize the fruit in any way, and we dropped them into bottles with unsanitized hands). We used organic raisins with no sulfites or preservatives.
I also have not found any inconsistencies with the carbonation. We did not pick through the raisins to find like sizes -- we used whatever we grabbed, but only 3. Smaller, larger, medium, whatever. The odd thing that I have been finding is, as I pour the beer, and subsequently the raisins, all 3 of the raisins have swelled to almost exactly the same size.
I am interested to hear what others will find. It seems as though there are a few other people out there that are giving this a try. I say it's worth the experiment. I have not, in any way, found this practice to ruin the beer.