I know quite a few people who have had logic board failures in all iMacs starting with the G3. Most likely it is from heat in tight quarters. The new iMac is a beauty, but I want a computer that will live for more than 2-3 years without Apple maintenance, so I will have to pass on it.
My Apple Blue and White G3 towers keep right on going and going. My 400 mhz has a new 120 GB and a 40 GB hard drive and a new DVDRWCDRW drive & loaded with memory, all installed by me. My 350 mhz B & W tower has a new 40 GB HD and the original CDROM drive. When I need speed to watch a TV show on computer, I turn to my Compaq with a 2.41 Ghz Athlon 64 processor. Even though OSX is superior to Windows XP, I can still use XP. I would not touch VISTA for any reason.