Yahoo! has apparently come to the conclusion that since so few uses Boolean anyway, they may as well not support it. That is a mistake. Power-users like librarians, journalists and researchers use them, and they are exactly the kind of people that influences the public opinion in these matters.
If you are a newcomer to the SATisfiability problem, you might want to take a look at wikipedia's page on the boolean satisfiability problem first. You might also find those surveys of interest. For a deeper insight of the current interest on SAT solvers for software and hardware verification, Armin Biere's course on formal systems is a good start. Eugene Goldberg has also a nice and somehow non standard way of introducing modern SAT solvers in his three part course on SAT.