My only real gripe with Win8 is the constant side scrolling one has to do in some of the Metro UI areas. On a touch screen with an accelerometer this makes sense because with a quick flick left you can quickly get to where you want to go but on a computer screen with a mouse its not so quick & easy. An example for this is the Market, you have to do constant side scrolling to get to items that interest you and by the time I got there I was ready to throw it out the Window. The same applies for the replaced start menu once you start installing all your games and software to get to them is a lot of side scrolling, yes you can make them favorites and they show up right in front but you still have to do the whole schlep of getting to the app.
My final gripe with it is the lack of customization or the minimalist look, my current desktop has a cycle change of the wallpaper every 30 minutes and has 4 icons on the desktop so its clean and (time to get flake from rusty & hamin
) pleasing to the eye to look at, Win 8 just has tiles after tiles after tiles of apps and it looks fugly to my eyes and I missed my wallpapers badly. Yes I can still access the old desktop but that is not the point since the first screen that greets you is a busy tile based screen and in the morning I dont want to see something busy and cluttered.
I wont upgrade when it first comes out because I dont need to, my current setup suits me perfectly. When the change becomes inevitable then and only then I will change, like if there was a new DX version that Win7 wont be getting.
*edit*
Just saw the pricing for the upgrade and its not to bad. If it weren't for other external factors in my life I would probably get it...