People who wanted to show their appreciation of the forum, but obviously nobody donates nowadays, and it goes to the forum fund.
Yes I know that it has been said many times that he is not going to lower the threshold, however I have also seen a post of his that said that he promised the donators that donations would go to forum development and hosing and to support the forum; however he has indicated that he is interested in using some of the forum money for community development but would need to get the donators' agreement before spending donations on items other then the forum (he still has ad money that he can spend on this first); adding a lower donation threshold could allow for him to mark future donations to be used for community development (or something broader then "forum development")
Good idea