We (technologists in general) are not always doing such a great job of graceful degradation, and it's hard to realize that if you're following along, upgrading software every year and hardware every 3–4 years. I dug an iBook (ca. 2001) out of the closet, it had Panther (10.3), which has Safari 1.x and won't run Firefox 3.x or Flash player 10 or Quicktime 7 (needed for more applications than you would think).
This machine will supposedly run Tiger (10.4), so that might open up a lot more possibilities for upgrading software. Or there's Linux. When people say Linux “breathes new life into old hardware,” I think this is what they mean. The software dependencies are less complex, and you can still get any version of anything.