I just traded my 4 1/2 year old Mac Mini for an iMac. While still functioning, for the most part, and was running Leopard and iLife '08, it was VERY slow. It was taking forever to load multiple things and basically, it became obsolete. It would've been fine if I was just using it for basic internet and surfing, but I was using the calendar and itunes and everything to run my phone. I still have a powerbook G4 that I use for basic internet and word processing and while it is old, it's not that bad.
As for the Mini in general, I loved it! Why would you spend $200 on a used one when you can get a brand new one with a lot of features for like $600-$700? Personally, if you have the monitor and all the equipment to run a computer, I would say go with a brand new mini. The reason I didn't was because it was time for me to upgrade to an iMac. I really liked the portability of the mini, which sounds ridiculous, but let me tell you, it came in handy.
My dad is somewhat of a computer guru and i had major issues with my mini in that the hard drive was corrupted. I just packed it up in a little bag and off I went to my dad's and he recovered the entire computer. It was easy.
If you want a brand new Mac and don't went to spend a ton of money, I recommend the Mini wholeheartedly.
