This is true, I have little or no contact with these people all year. We used to get together for Christmas but no more. The only time we do get together is if they are having some sort of party which is usually a gift giving occassion (graduations, etc). It does seem silly to continue with the gifts but if they continue, I feel like I should. BUT I have a real hard time sending someone who is over 18 a check. At that point I consider them an adult no matter what 'stage' their life is in. I also feel like I can't continue with the oldest as I have already stopped the gifts for his cousin who is a year older in another family.
Just a side note. For all the years we have been giving Christmas gifts, I have received just one Thank You note...it was last year...it was written by their mother.