I've been reading about the CD/DVD eject problem for the last few days (I don't even have an iMac, I just can't help but gather knowledge about Apple everywhere), and it seems to be isolated to mass produced CDs/DVDs that either have a thick layer of ink on them, or CDs/DVDs to which a label has been affixed.
On a side note, I would never recommend affixing any kind of label to a CD, especially one that doesn't cover the entire CD (they can throw the balance of a CD WAAAAAY off and cause damage to your drive over time) and I wouldn't even recommend the entire-CD-labels, either. CDs aren't checked extensively for stability when rotating, but putting any kind of label on them is sure to throw them off-balance: something that is necessary for proper operation.
That being said, I don't want to jinx anyone with a new G5 iMac, but for Apple to get the price as low as it is, I wouldn't expect the case or structure of the iMac to be very strong. The G4/G5 cases are like blocks of steel -- you can throw them across the room and they'll survive. I would also assume that the internals of the iMac, while powerful, may not be up to the stringent design inherent in the G5 cases. It would be easy to overheat an iMac, simply by placing it in a situation where there wasn't adequate ventilation near the top exhaust slots or using it in environments like many college computer labs, where many computers reside in a room with only the standard A/C ventilation. If you've ever ventured into one, you'll know what I'm talking about -- they're usually pretty stuffy with a lack of ventilation.
I think the same of the eMac -- while it's a great all-in-one design suited perfectly for classrooms and labs, I don't think the environmental tolerance of the machine is anything NASA would want to take a look at.
For example, I've got a friend that I'm fixing an old B&W G3 for. His fans are caked with dirt, and the power supply fan went completely kaput. His ethernet port stopped working -- I assumed from a power spike at some point, which he had a lot of, but it wasn't that. The computer would power up just fine, but the power supply fan wouldn't spin and the ethernet port, when viewed under the Network pane of System Preferences, would blink on and off intermittently. Replacing the power supply fixed the port... strange, eh?
If you've had problems with your eMacs, I would first take a look at the environment they're used in (and I'm not making any accusations, just suggestions). Is it difficult to cool the room? Is it noticeably warmer than adjacent rooms? Are the machines placed closely together, and is there at least a foot or two of space around all sides of the computer? Are the computers placed in such situations that a "hot-box"-like effect would happen (common with computers placed in "cubby-hole"-type desks, where there's a shelf above the monitor/computer and desk "walls" on either side)?
At any rate, like I said before, I don't think the new iMac G5s will take a three-foot drop to the floor, but from what I've heard, the screen is great, the speed is great, and the form-factor is great. I suppose we'll need to wait another month or two for the possibility of a report of short-term failure, but I'm hoping we don't hear anything.
