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Never had a Mac (buying my first in the coming days) but iv kept my windows machines until they died, usually it's the system board so I salvage the hdd and recycle the test. Once I get the Mac up and running my windows machine will either be used when I need to due a BitTorrent or I will give if to my 9 year old twins since my 13 year old is getting his own machine for his birthday
 
I'd just like to say for those who are keeping their old computer as a spare in the closet, you are most likely wasting a valuable commodity. Either make use of it or give/sell it to someone who will. Don't be adding to electronic waste crisis.

It's still going to become waste eventually.

I don't give my stuff away for the same reasons Marty62 mentioned. These people need professional grade machines, not last year's hottest laptop.
 
Giving away to others ... Direct family, neighbors, colleagues. In few cases to professional recycler/e-waste collector (where I have to pay).
 
I sold my late 09 27" iMac yesterday for $950, just use m 15" MBPr now, not bad after 4 years use.
 
I always kept my last Mac as a backup, with the quality control/drivers going sideways with Apple lately *cough* 2013 MacBook Air(wifi & audio issues) *cough* and the 2012 mini HDMI glitches I'm not into taking blind risks with a new Mac. (PowerPC era you had the fewest driver hell moments on new model launches)

As far as "retirement", my older PowerPC Macs had their RAM, HDD & ODD stripped out for spare parts/trade purposes and leftovers junked. My only pre-OS X iMac had been rebuilt from spare PowerBook G3 parts via trades(traded PC100 DIMM ram for PC100 SO-DIMMs, faster CPU card and re-wired a PBG3 DVD drive to work in a tray-loader iMac)

Sooner or later any electronic gadget will hit the recycling/ewaste bin.
 
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