This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
Frank, As a machine is on, more and more things get cached. After a reboot, the cache is completely empty so everything you do is a disk access. This has the effect of making things signicantly slower until enough is cached again.