I have personally used Windows 3.1 through Vista (just about every version), a smattering of OSX on other people's Macs, and some Linux (Ubuntu, Debian, Damn Small Linux, and Puppy). I'll discuss OSX first, as I have the least to say about that.
My only experience with OSX is on my friend's iMac and MBP, my friend's dad's Mac Pro (Final Cut Pro is made of win) and on my cousin's MacBook she just bought for school. I like it, but I haven't really used it enough to have a good opinion of it yet. I don't understand the mac-haters at all though. Apple's hardware does cost more; get over it. Their laptops aren't nearly as bad as their desktops though, in that area. Any quality laptop will cost a premium. (Although the Macbook Air is just silly.) And people who say that Apple should release OSX for non-Apple hardware need to realize what they want. One of the main reasons that Apple's OS is as stable as it is is that Apple designs their OS around their hardware. If Apple were to release OSX for vanilla PCs, they would need drivers, lots of drivers. Which would create massive compatibility confusion and lots of headaches for Apple. I seriously doubt that they would go through all that. As far as iPods go, I like mine (iPod mini from about 3.5 years ago
). It plays music, has an easy interface, and syncs with my computer easily enough. Also, I've messed with an iPod touch, and they are just plain cool, although expensive. But an iPod classic is one of the best values in MP3 players at the moment. Zunes themselves are fine, but the software is terrible (it's like an unholy blend of IE7, Vista, and WMP11). Whatever though, this isn't an iPod/Zune discussion, so I'll stop here.Next up: Windows. Windows XP is a great operating system. Windows Vista should have never left Redmond. I've used XP for about five years now, and it's one of the best, most stable, fastest OSes I've used. I currently am using Windows XP on my Dell desktop (2.4GHz P4, 1GB RAM) and my Lifebook (800Mhz P3-M, 256MB RAM). It runs just about all the software I could ever want, and isn't a jerk about it. It doesn't look as pretty as OSX or Vista, but I couldn't care less (I'm using classic mode anyway; I'm not a fan of the Fisher-Price look). Vista, on the other hand, is total garbage. I haven't had to deal with it on any of my computers, but I have on other people's. A co-worker of mine installed Service Pack 1 on his laptop, and it broke the Wifi driver, rendering his laptop virtually useless. I ended up having to restore Vista to pre-SP1, and turn off automatic updates.
Also, it runs way slower than it should, given his hardware (core 2 duo, 1GB RAM). Also, the UAC is annoying, but easily disposed of. The interface looks nice, but I don't like how everything is moved around from where it used to be in XP, and how certain things are hard to get to (you have to go to an extra menu to actually turn off the computer, irritating. 
). Recently, a friend and I built him a gaming computer (E8500, 4GB RAM, Radeon 4850), and Vista took four tries to install (kept crashing/BSOD'ing), and then kept giving cryptic errors whenever we tried to do anything. The most amusing error was this (shown when we tried to play World in Conflict): "Windows cannot find "error". Please make sure you typed it correctly, and try again." 
Another reinstall of Vista fixed everything, but that was downright obnoxious. Once installed correctly though, Vista runs at a decent speed and stuff works fine. All of his hardware was compatible with Vista, and it was still a pain. Another thing that bugs me about Vista: It's making XP harder to find. My dad and I each bought an XP SP3 disc from Newegg on June 30. Some computers can still be bought with XP, but you have to jump through hoops or "upgrade" to Vista Business to get it. Luckily, my friend was able to get herself a Thinkpad T61 with XP without too much trouble. Anyway, that's enough about Windows.Now, Linux. I used Linux on my laptop daily for about six months. I tried Ubuntu, Debian, and Puppy on it. They all worked pretty well (with Puppy being crazy-fast). However, the ACPI drivers were not quite right. I couldn't use the mouse after resuming from a standby (hibernate worked fine). Also, in Debian, it took some doing to get my wifi card working correctly (no issues in Ubuntu or Puppy; worked out of the box). It worked, and it was nice to not have to buy XP for it. It was noticeably slower than XP though (except Puppy, but that was so stripped down that it doesn't count). I'm also using Ubuntu on my file server. All that computer needs to do is sit there and run samba, so I haven't messed with it too much there. Linux is fun to mess around with, and it's nice that it's free, but I don't think I'll ever really use it on a regular basis.
TL;DR: I don't have too much of an opinion on Macs, but I've liked the little bit I saw. XP is great; Vista is garbage. And Linux is "Fun to play with, not to eat."
if commodore hadnt been so stupid with their business practices amiga would probably still be as big a player now as they were in the late 80s and early 90s. there OS was the BEST. first with preemptive multitasking, dynamic memory allocation, high res and high color graphics, 4 channel stereo sound and it was FAST and VERY flexible windows could have different resolutions and color depths and run more than one application at a time. someone earlier was bragging that their OSX would boot in under a minute, amiga OS4 running on a 800mhz powerpc based computer will boot in under TEN SECONDS. 