Pros: Nice and fast; small footprint; beautiful industrial design
Cons: can be noisy; component failures on early production models
The bottom line: Do NOT buy 2004/early 2005 models used/out of Applecare warranty: High chances of failure of mid-plane/power supply.
There is no doubt that the iMac G5 is an excellent model, both in speed and in appearance. Price wise, buying an iMac G5 is even more economical than the purchase of a Mac Mini plus a flat screen, keyboard and mouse.

This model's footprint is so small, you will appreciate the reclaimed space on your desk.

For those switching from Windows, please note that the speed in GHz is insufficient to compare real-life speed of a computer since the processing power of a CPU chip and chipset technology (such as Altivec) also account for much. This iMac using a G5 chip and running OS X is blazingly fast.

Since there are some excellent full reviews of this model already on Epidions.com, I will limit my own entry to two important issues I have not seen covered there.

FAN NOISE

The iMac G5 uses a forced air system with an outlet at the top-rear of the case to maintain acceptable temperatures within the casing. Too much heat could cause component failure, and with such a tightly packed design heat can build quickly without proper dissipation. This is unlike the Mac Mini that uses Powerbook laptop components in a desktop enclosure, because laptop component were especially designed to limit the amount of heat they create.

While the iMac G5 is usually a fairly quiet machine, I found the noise it makes with the fans going full blast disquieting.

Fan management could do with some fine-tuning as well: Full fans activate not only when some processor-intensive tasks creates strain on the system, but almost randomly.

Perhaps later OS or ROM update will resolve the issue. Until then, there is little to do about it.

BREAKDOWN

The second issue with these Mac is far greater; it has to do with a little piece of circuitry called the mid-plane.

The Mid-plane has failed in more than a few instances, where the first warning is a nauseating smell of burning rubber, soon followed by a dead Mac.

In case of failure, Apple will ship you an early replacement and guide you in changing the part; your credit card will only be charged if you fail to return the original part after the switch. But we have had to follow-up on multiple users still with problems even after the mid-plane has been replaced.

Matt Neuberg in the 25-Apr-05 of TidBits mentioned three potential issues: The mid-plane and the power supply, plus a domino-effect failure of both.

These failure are more than anecdotes, and have struck a large number of machines in the 2005 production. I would like to believe it has been resolved in the late 2005 production models, and it may very well have been since reports have started to dry out.

My suggestion is simple: If you purchase an iMac G5, avoid buying it second hand unless you get a too-good-to-pass deal

BONUS FEATURE - QUICK TIP

Finally here is a quick tip for saving money and getting extra performance: The iMac G5's bus throughput is accelerated by RAM being installed in matched pairs. Ideally, get a pair of identical memory at purchase time OR, get the default memory and buy a matching pair at the same time later.