Our computers:

1 2005 Mac Mini G4, starting to show signs of giving up the ghost. Plus, we can't update a good deal of the software on it any longer. I'll probably either Freecycle it, give it to a neighbor, or sell it on Craig's List.

1 2006 MacBook Pro, soon to be replaced because it's limited to 2G of RAM and useless to me now as a portable development machine. The damn thing runs hotter than a jet engine too. I haven't replaced it yet mainly because it has a gorgeous 17" matte screen and the best keyboard Apple has made to this date.

1 2006 Mac Pro, still going strong and used as my main development machine.

1 2007 iMac, my eldest son's machine, which will probably replace the Mini downstairs when he goes off to college this Fall. Hmm... maybe I'll give him the MBP... the only problem with that is I'd want to replace the hard drive with an SSD first because he's death on electronics.

1 2009 MacBook, my wife's machine, works just fine and no need to consider replacement.

I keep computers as long as most people keep cars (my current car is a 1997, incidentally), and replace them only in dire necessity. In my experience the Mac hardware keeps its usefulness longer than PC hardware manages. But then again, I stopped buying PC hardware years ago so what do I know. ;-)

Not everyone is a gotta-have-it fanboi.