Donald Knuth, in the preface of each of his books, and also on his website, offers to cheerfully pay a reward of $2.56 to the first finder of each error, whether it be technical, typographical, or historical. For those who have to ask, his FAQ explains that 256 pennies is one hexadecimal dollar. An article in MIT's Technology Review describes these reward checks as "among computerdom's most prized trophies" http://www.technologyreview.com/view/article.asp?p=11380. As of October, 2001, Knuth reports having written more than 2,000 such checks, with an average value exceeding $8 per check http://www.ams.org/notices/200203/fea-knuth.pdf. The "History of TeX" explains that "Knuth's name is so valued that very few of his checks — even the largest ones — are actually cashed, but instead framed." http://www.tug.org/whatis.html

The reward for coding errors found in Knuth's T_EX and METAFONT programs followed an audacious scheme apparently inspired by the Wheat and Chessboard Problem http://mathworld.wolfram.com/WheatandChessboardProblem.html. It started at $2.56, and doubled every year until it reached $327.68http://www.ams.org/notices/200203/fea-knuth.pdf. Recipients of this "sweepstakes" reward include Chris Thompson (Cambridge) and Boguslaw Jackowski (Gdansk) http://www.uni-giessen.de/hrz/tex/more_info/info/mailarchiv/mutex.1995/msg00147.html.

Intelligence: Finding an error in a Knuth text.
Stupidity: Cashing that $2.56 check you got.
Seen in a Slashdot sig, quoted by Edward O'Connor
(source http://www.stgray.com/quotes/programming.html)

Each check's memo field identifies the book and page number. 1.23 indicates an error on page 23 of Volume 1. (1.23) indicates a valuable suggestion on that page. Such suggestions are worth 32¢ each. Note: Θ denotes the book Things a Computer Scientist Rarely Talks About, and KLR denotes the book Mathematical Writing (by Knuth, Larrabee, and Roberts).

Frank Ruskey's class with checks

Some reward checks include interest compounded continuously http://www.math.rutgers.edu/~zeilberg/mamarim/mamarimPS/king.ps.

On July 1, 1996, Knuth sent out more than 250 letters, 125 of which contained checks, for errors reported in The Art of Computer Programming since the summer of 1981. A few of these remain unclaimed http://www-cs-staff.Stanford.EDU/~knuth/address.html. This article is licensed under the GNU Free Documentation License.