In 'Life, the Universe and Everything' Arthur and Ford land on Earth in the distant past and discover that humans are in fact descended from the Golgafrinchans who crash landed on Earth thousands of years ago. So, the ultimate question could never have been found that way because the whole experiment was tainted.
BUT because of this, Arthur and Ford decide to create a random question using scrabble tiles and the original Earth inhabitants to pick the letters. They come up with the following question: 'What do you get if you multiply six by nine'. Which proves that the universe is inherently flawed says Douglas Adams.
Bit of a let down that wasn't it :)