I'm definitely going to do this:
My advice? If you buy an iMac, get it set up, run Software Update, then run Apple Hardware Test. (Put in the DVD that came with the computer, restart holding down the Option key, click on AHT, click the next arrow.) Run the 'extended test', which will take 30 minutes or so. If it reports any failures, take the computer back to the Apple Store and exchange it for a new one.Apple probably took a bridge too far when they put the G5 and a modern hard drive in this enclosure.
Update: If you want to run the hardware test repeatedly, type Ctrl-L to switch AHT to loop mode. Also, if you're accustomed to earlier versions of AHT, you may wonder how to get started. The directions are in small print on DVD 1 of the 2 DVD set. It takes a LONG time to go through the AHT selection and startup process; be patient. The machine is not dead, it's just .... thinking. A lot.