Windows Vista... The OS that has been criticized for a shitload of things that are way too much to mention here. HOWEVER, as an user since the RC1 phase I'm writing about the few misses that I've experienced.
1. Maximized = Black: At first, I thought this was a bug during the development of Vista. I was full of hope that they made it transparent for the RTM version, but we were stuck with a black BG that varied depending on the color chosen. Some people like the black, some people don't. I wish that an option for choosing between those two would have been awesome.
However, with stuff like VistaGlazz, those few sentences were a waste of my valuable time :D.
2. Windows Explorer: I must say, Microsoft did an awesome job redesigning the Explorer UI. However, there is one thing that really sets me off, and that's how Explorer works . In my experience, it feels like it's trying to read the files the same way a PS2 loads data. It's slow as hell! But after using Windows Server 2008 x64 that problem has almost been solved. (In there, not Vista)
3. People complaining about UAC: This isn't directly about the OS, but damn! Some people just complain about it to no end! Seriously, the first time I used Vista I just couldn't stand it and turned it off. I was like "There, problem solved.". But some people just stick with it and whine. If you don't like it, just take it out!
There, thats about everything that irks me. I like Vista and it's difficult to stick with XP, but with some fine-tuning, it could become way better.