Sadly, I upgrade my PC about once a year due to neccessity.
Otherwise, salt corrosion will eat it up (I live near the pacific ocean). Here's what happens: PC's work fine for about 10 months, then all of the sudden, weird things start to happen, then they eventually crash. I've since installed A/C and air filtering, but it only slows the inevitable.
I just had my first occurance last week (on my Aug 2006 PC). PC wouldn't POST. Ended up having to replace the mobo...$180. When I was disassembling the PC, I found a huge clump of salt crystals in the case on some of the cards. Youch!