Written: Jan. 10, 2008.
My first exciting discovery was Aviezri Fraenkel's middle name, that I found in both wikipedia and the mathematical genealogy project. Since I knew that Don knows Aviezri personally, and he always asks for middle names, I asked Aviezri how come his (alleged) middle name is not listed in the index of ACP. Aviezri replied that Don indeed asked him, a long time ago, and Aviezri replied that his middle name is just the one-letter string "S". A careful look at the index revealed that Knuth accepted this unusual middle name, and the index entries are "Fraenkel, Aviezri S" and not "Fraenkel, Aviezri S." . Whether Aviezri's middle name is indeed just "S" or is longer, is still an open question. If this is the case, it seems to conflict with the "Aviezri S. Fraenkel" in Fraenkel's numerous publications, the period in "S." denoting, according to common usage, a word properly containing S. Be that as it may, it shows that Don's respect for people's wishes even surpasses his desire for accuracy.
A more challenging project was to find what the "M." in "Roger M. Aarons" stands for. I googled the latter, and found out that he was a member of the renowned Stuyvesant High school Math team, back in 1957, and discovered some names of teammates, one of them being Monroe Rabin, whose E-mail was easy enough to find, him being a well-known physicist at UMass, Amherst. He lead me to Roger's phone number, whom I called, and left a message with a request to E-mail me with his middle name. It is Michael.
I had an easier time with the First name, of "C. Haros", being "Charles", as a quick look at the catalog of the Bibliothèque Nationale showed. Even easier were Arthur Bertram Kahn (catalog of Johns Hopkins University, where his Ph.D. thesis is listed), and William Morton Kahan (Math. genealogy). In Concrete Math there is a J. Garfunkel, a teacher at Forest Hills High School, who proposed quite a few Monthly problems, and a quick internet search revealed that it was Jack Garfunkel, not to be confused with a certain Forest Hills salesman of the same name, who happened to be the father of an obscure Forest Hills High school alum called Art Garfunkel.
Alas, it turned out that all this effort was probably not necessaray, since Don, most likely, knew all these names all along, since when I looked up his website's call for help, he listed some real challenges, and none of my discoveries are listed there, implying that he already figured them out by himself, or with friends' help. I am completely clueless about the listed names, and it would take much more than a casual internet search to uncover them.