My main desktop is a Dell Precision 360, dating from around 2003. Currently I have a programming IDE, Skype chat, two terminal windows, five Firefox windows and a couple of Open Office documents active. I have no virus problems and my current set of software was zero-cost.
My test servers, mainly Apache2 and MySql [going to Drizzle now that Oracle bought Sun, though] are also this kind of age. The only exception is a low-power Sheevaplug with no moving parts and 7watt draw that I use to plot temperature.
How is this possible when big organisations change their systems and software about every three years? When half the networks and systems are virus-riddled and take 1/2 hour to boot because they are loading huge remote profiles?
The general answer is open-source and in particular Ubuntu Linux. I’ve gone with that because it’s pretty mainstream, there’s good package management and community and the desktop is pretty good.
It costs a huge amount of resource in minerals, energy and water to create a PC. Then it costs another amount to ship it to be stripped down, wasting many of the parts and creating toxic waste, in the process.
So the simple answer is use until the ‘real’ end of life. Or let someone else use it, if you must insist on the latest, shiniest, most inefficient and virus-prone toys. Your call.