Conventional wisdom: recycling is typically the best option for the stuff I don't want anymore.
Little-known factoid: recycling a PC consumes 20 times more energy than reusing it, according to a study by Eric Williams for the United Nations.
I was pretty stunned when I read that fact, too. As fun as it is to upgrade to the fastest machine I can get, figures like the above give me pause when I think about upgrading and disposing of my older PC. It also makes you realize the incredible environmental impact that Microsoft is belching onto the planet by producing such a lousy piece of bloatware that is Windows Vista. Just think about how many PCs were made irrelevant in the eyes of their owners when they chose to upgrade to Vista, as well as how much energy went into the the recycling of the 'old' PCs and the creation of their replacements. We should tally it up and send Microsoft the bill for the economic externalities it dumps onto society.
Luckily we Linuxers have more options. We can obtain those old PCs and load Linux onto them, which is certainly lighter than Windows Vista. Furthermore, if the PC is creaky old, we can install Linux with lightweight desktops like Xfce.
Now I only wish we could somehow install Splashtop onto older machines. Splashtop is a Linux-based application that you can boot right into within few seconds (even if it's a Windows machine) without a full-fledged boot to access core applications like Firefox, a mail client and Skype. I would go out and get a bunch of old laptops and have them around the house for spur-of-the-moment Web and email access.
Wouldn't that be a great use for our old hardware?