This isn't a 'windows sucks, use something else' reply. Personally, I like Windows 7 and the only pop-ups I used to get could be disabled in UAC.
But, how much windows only software do you use? Ubuntu is free and is pretty good. I use it 90% of the time (quite a few games won't run it so I use windows 7 for that aspect). Initially I used it as I do a lot of coding and linux is generally better for that, but now I use it because I prefer it to windows. Ubuntu 10.04 looks nice, is easy to use and automatically does loads of driver installs for you. Also, if you don't mind using a command line you can use 'apt-get install' which will download and install software for you which is pretty nice!
Ubuntu also has WINE (windows emulator) which can handle a lot of windows software pretty well these days. Try out an Ubuntu Live CD, it lets you get a feel of Ubuntu without having to install anything. If you don't like it then you haven't spent any money or lost anything and can continue to buy windows 7 :).