My 2005 PPC iMac still runs although I don't use it now. It did have the blown capacitor problem but Apple replaced the logic board & power supply even though it was out of warranty.
My parents have a 2006 Intel Core Duo iMac which they still use every day with Snow Leopard. It had the vertical lines screen problem but Apple repaired it --4 years after it's purchase.
A friend of mine still uses a 2007 Core2Duo, I upgraded the RAM and the OS to Snow Leopard for her 2 years ago and it's running great.
She also had another identical 2007 iMac in the original packaging, never opened and set up,
AND a sweet little white 2007 Mac Mini ---also in its original packaging and never removed ----which she handed off to me last week to set up for her with SL & more RAM etc.
Unfortunately the iMac doesn't boot up --just the white light, so we'll deal with it a little later, in the meantime I pried open the Mini to replace the RAM, etc. and it's all ready to go now. Even though both models are "brand new" from 2007 it was really thrilling to unbox them.
I love my more recent 2011 iMac but the white models have a big place in my heart. I wish my new aluminum iMac "breathed" when it sleeps.