I set up the Mac Mini, and so far it is going over well. I myself am an OS X novice so I have to experiment to figure out how to do stuff. For example, I don't know how to enter an accented e in "Exposé", my favorite OS X feature so far. (NOTE: thanks to Mac expert John I can do it now!) I could use Exposé at work where I usually have at least 8 or 10 apps going. Instead, the Windows alternative is Alt-Tabbing through all running apps to find the one to switch to, and that isn't as fast or easy.
After using the computer for a few hours, I think it is really sweet: compact, attractive, VERY quiet, easy to use, powerful enough for typical usage. Argh, now I want to get one for myself! It is going over well with my parents, and I see getting my aunt and grandmother one eventually.
A pleasant surprise is DSL - now offered where my parents live, and they signed up for it. Since they have broadband I also bought them a wireless router. What a change, from dialup on Windows to broadband on a Mac!
The acid test will be if this computer resists spyware/viruses and generally remains usable months from now. Unfortunately my parents have spent way too much time, effort, and money keeping their old Windows machine creaking along.