iMac G5 behaving erratically!

Earlier this year, my iMac G5 (Power pc) melted down. The logic board was gone, and I was quoted a $1200 fee to repair. The computer was just over 3 years old. I contacted Apple, who agreed to pay for the repairs.

My question relates to my sister and her husband's iMac G5 (intel), which they bought on my recommendation in April of this year. Unbeknownst to me, they had their machine into the shop this summer and paid a $300 repair for a hardware malfunction. (not sure what) Of course, this was just after the one year warranty expired. They are now experiencing a lot of freezes and generally screwed up behaviour with their computer and have asked my advice. Which was to take it into the shop and find out what's wrong and then contact Apple.

What I would like to know from the discussion group is if there are a lot of known hardware problems with this generation of the iMac G5, as there certainly was with the one I bought.

The technician who is servicing my sister's computer has run a diagnostic program, and has found nothing wrong, and so is suggesting a 'software problem.' I am skeptical given my experience.

Any suggestions would be much appreciated.

thanks.