With a little help from the Google search engine (the irony!), I have found the sources of "inspiration" for the questions asked in the "Google Quiz" (GQ) in the recently concluded FOSS.in 2005.
The first problem was the same as #2 in the problem set for the 9th World Puzzle Championship (Qualifying Test) (PDF). The second problem was the same as #2 in the 2002 US Championship Puzzles. The third problem was the same as #1 in the 2000 US Championship Puzzles. The fourth problem was essentially the same (verbatim, except for the actual numbers) as #22 in the problem set for the 10th World Puzzle Championship (Qualifying Test) (PDF).
Not being someone who solves puzzles regularly (except for Sudoku, of course), I was quite impressed by these problems since most of them involved considering multiple alternatives, proceeding with one of the alternatives and then backtracking and proceeding with another if that proved invalid, continuing till one finds a solution. They should also be fun to solve using computer programs. (I know of at least one person who did precisely that.) I had asked some of the people at the Google booth if I could reproduce these puzzles on my web site to share with my friends, but they were not sure of the copyright issues and clearance for publication. Well, now we know where they got the puzzles from and have found some more interesting puzzles to work on!