I picked up a couple of old Macs this week. The first was a Powerbook 1400 that the owner didn't know if it worked, he didn't have the power adapter. Plugged in an old yo-yo adapter and it fired right up. A blast from 1997, 15 years later, still running well. Hearing the chime, and the hard drive starts spinning up, and then the screen comes alive, that's fun to me.
My original 1984 Macintosh and SE both still run great and are knocking on 30 years old. 30. It's almost impossible to even find a dead Windows PC from the 80's, forget finding a working one, but you can find old Mac's and Apple II's that are still running strong all day long. It's similar to the video came consoles from the late 70's/early 80's. Atari's are pretty rock solid and keep on working, decades later, but what are the chances of an Xbox 360 or PS3 still working 30 years from now? Even if a working Xbox 360 survived 30 years, Xbox Live would be long gone. But you can get a 30 year old Mac to run on the Internet. Some Mac websites were hosted on Mac SE's, there might even be a couple left still running off an old SE being used as a server.
I also picked up a Tangerine iBook, the original 300mhz model. I always wanted one. Tonight I installed a dual boot of 10.3 and 9.2.2 and it's surprisingly fast, including surfing the web, as long as it's not asked to multi-task.
That's the one thing that has always amazed me, how fast some of these ancient machines still feel. Tiger on my Pismo laptop is extremely fast at the 'blistering' speed of 400 mhz. I had a 1.33 Ghz iBook a couple of years ago running Tiger, but the Pismo feels much faster.
My daily driver is a 2011 Mac Mini Server, but as wonderful as that Mac is, the old ones have more charm. It's fun watching the old keynotes were Steve Jobs introduces them, and while I could never afford any of them when they were new, today most aren't worth $100. I use them for a while, keep the ones I love, and pass the rest on to family/friends or end up selling them, but just because something is old doesn't mean it has no value and can't be useful.