Larry - I don't think it is that people don't enjoy "sharing" info. I think it is also about someone willing to take a few minutes in their busy day to post a comment or update info about a cultivar.
It seems that when a raffle is coming up, people are more inclined to add to the database to earn some quick acorns. At least that is what I have noticed. Maybe I am wrong as I don't have the number crunching to know for sure. Dave would know. I think that is the main reason he does the raffles. To motivate people to add to the database or write articles for ATP.
