I'm surprised that everyone who has responded to my post has defended the
conventional wisdom on charity giving. But surely one should either borrow
money to do a life time worth of giving right away, or save and do all
charity in one's will, or otherwise concentrate all charity giving to a
single moment in time.
Given Robin's comments, I'm not sure anymore when is actually the best
time to do the giving, but it cannot be optimal to do what many people
actually do, which is to give a percentage of one's income to charity as
one earns it.
This point is very similar to the one Steven Landsburg made in one of his
Slate articles, http://slate.msn.com/id/2034/, which was that a donor
should give all of his contributions to one charity, and not spread
them among several. The logic is almost exactly the same.