I bought an Acer Aspire One about 4 months ago. It has been a great little machine for me. It comes down to your needs and what you will be doing with it. I wanted a robust laptop that I could take anywhere with me, and the Acer meets that. It does not have an optical drive, however, I have not missed it. It does have two flash memory readers to make up for it. Everyone that sees it thinks it is a toy until they use it. Then they want it.
CNET Review
As for Mac versus Windows, I built my PC and have a Mac Mini sitting next to it. The Mac OS is not inherently more stable than XP. Neither of mine have crashed in months. I have had crashed on both, just not frequently. If you know what kind of software you are putting on Windows, and if you know what you are doing, it will remain just as stable as the Mac OS. That being said, I am currently using Ubuntu 8.04 on my PC (2 weeks going strong), and it is far better than either XP or the Mac. You can add all of the pretty features that the Mac has, yet keep all of the openness that the PC has. For me, it is the best of both worlds.