Google answers The Great Question

Yes, Google knows the answer to life, the universe and everything! (via Las Penas del Agente Smith)

But if you are looking for something more useful, you can use Google Calculator. Simply enter the calculation you want to compute in the search box. It has lots of useful operators and recognizes most common constants and units, and can do unit conversion, among other things. If you are using Firefox this becomes specially useful, as you can use the Firefox search box as a calculator. For example, input 2004 in hex in the search box, press enter and, voila! 2 004 = 0×7D4. Neat.