I'll bite.
As has been said pretty much any OS will work for basic web surfing, IMing, and email checking. I'd probably using Ubuntu full time if Flash worked as well as it does on the other platforms that being said an OS is a personal choice what ever works best for you. Each operating system has it's own set of negatives and positives which are relative to personal preferences.
I bought a used Mac Mini earlier this year just to test out the Mac side of things, I upgraded to Snow Leopard in September, over all I find SL a little snappier than Leopard but not much over all.
I like Macs because The GUI is just easy on the eyes and pretty much every app conforms to Apple's GUI guide lines.. It's cohesive all apps act as expected from one app to another for instance Cmd , always brings up the apps preferences. The included apps with OS X are actually useful. Most open source software available on Windows have an OS X port. Time Machine takes something as mundane as backups drop-dead simple and full of eye candy. I also like the fact that despite having less memory and a slower processor my Mini runs faster than my laptop running Windows.
I dislike Macs because there aren't all that many great free apps aside from the aforementioned open source apps. It seems that the really awesome/useful programs are paid and the price tag often isn't cheap. The Mac world is a lot more 'closed' then the windows side. Accessories made specifically for Mac seem to carry a higher price tag than Windows.. Try finding a $20 Webcam for Mac. Also Macs are prohibitively expensive, IMHO. The fact that OS X can now run on any Intel box and Apple explicitly forbids running OS X on non Apple branded machines really doesn't sit well with me.
I like Windows because no matter what you plug-in it's pretty much guaranteed to work. The hardware Windows runs on ranges from old and cheap to cutting edge and expensive. The ginormous variety of both free and paid software. By being familiar with Windows allows me to jump on ~90% of the world's computers and instantly know how to navigate and do stuff. Lastly, Supporting Windows users makes me money.
I dislike Windows because of the constant stream of security patches and the need to run AV, which takes resources away from doing computing that I want to do. The price tag is expensive when compared to OS X (arguably though the price of Mac hardware is expensive to cover OS X development), DRM BS like Media center's saving TV shows in a locked down format, to me that shows MS has put the needs of corporate strong arms above those of it's home customers. The included software with Windows is practically useless I assume this is so you'll buy Office.
I could add Ubuntu into the mix but it's probably not worth it for this post. :) As I said above an OS is a personal choice and I choose to use Windows as my main web development box and my Mac for email, IM, facebook, etc.