Personally, I have a pet peeve about throwing out perfectly good working hardware. I still use several PPC systems. They're not really relegated to anything important, and they certainly can't be used for something like watching Hi Def video on the web (mine are all single core) but you can always find a use for them.
For example, I have an old Titanium PB that I use in the morning when I wake up to do a quick e-mail check and check the weather. It's perfect for that.
I have a 1.33GHz 12" PowerBook that's connected to a large FireWire hard drive and a printer. I use it as a base station for wireless master backups and a print server. It works great. You don't need a "killer" machine to do any of these sorts of tasks, and why put strain on newer systems if you can offload some of that work to a system that a lot of other people see as a throw away?
I can probably pick up an 867MHz 12" PB for about $50, and I'm considering connecting a USB camera to it and feeding the camera to the exterior of my main doorway. We get a lot of really obnoxious salesmen showing up at the door, and this would give me the opportunity to run a program on the unit and when someone rings the doorbell, just pop open the lid and see who it is. If it's a neighbor, someone I'm expecting, a delivery person...in other words, those that are welcome, I can open the door. If it's yet another obnoxious salesman trying, once again, to sell me new "thermal" windows or a new roof, even though I already have both, I can miraculously manage to not be home at that time! You don't need a MacBook Pro with a Retina display to sit their and do essentially dumb work.
Interestingly, none of this sort of use would ever show up in web site statistics. You can always find some use for outdated hardware if you're creative.
