I, too, agree with The_Techie...
Mark Shuttleworth put it best when he said that the ones who will benefit most from Ubuntu are those with VERY LITTLE computer knowledge and those with A LOT of computer knowledge. The ones who are in between get frustrated because they don't understand how the background mechanisms work, and they aren't willing to put in the hours to figure it out. Those people should stick to what they know, whatever it may be (Windows, Mac OSX, etc).
However, for those who have very little knowledge of computers, they won't mind either way. They won't be able to set up Windows either, and if something broke on Windows, they wouldn't know how to fix it. Likewise if they needed to install new hardware, configuring the devices would not be an easy task on Windows.
I agree that there are some compatibility issues with Ubuntu that many average users find frustrating, but a wealth of information is available on the web (especially at ubuntuforums). And if your hardware is supported, then there are NO problems.
I've installed ubuntu on... um... upwards of 20 - 30 different computers with various hardware configurations, and have never found a deal-breaker. The main issues are with unsupported wireless cards, strange sound setups and (until recently) ATi drivers.