I sort of like Steve's description of caviar although I have to say they don't quite taste the same. I have received a lot of responses on this one and they are all over the place. Not sure I can even sort out the serious from the jokesters. A few things I can confirm, they are not lead as some have suggested, they are magnetic. They were not left over from bead blasting as some have suggested. They were intentionally packed in the BB almost like you see wet coffee grounds packed into something. The folks with the scientific explanations went way over my head. The suggestion that it might be a clever rust inhibitor mechanism or oiling method seems plausible. The use of these as some sort of prank even sounds possible. The intentional weight addition to the frame can go either way.
I just added photos of the entire spindle, bearing and interesting washer combo to the site. You will notice a pair of brass washers that were used to keep these from getting all over the bearings, at least I think that is their purpose as I see no other reason for them. Here is the link with added photos.
http://pg.photos.yahoo.com/
Keep those suggestions coming as it is both interesting and I am going to compile a list of them to review at a later date. Sure would be great to find some documented evidence of their use or existance on bicycles.
Ray Homiski
Elizabeth, NJ