I upgraded my computer from Windows Vista to Windows 7 the day it was released, October 22. I didn't have any particular complaints about Vista, except that it tended to be a bit on the bossy side. Windows 7 promised to be a bit less bossy as well as slimmer, hopefully resulting in quicker boot times as well as faster program launches and operation in general.
Windows 7 also has some neat usability features and I'm pretty happy with the upgrade in general. But (you knew there had to be one, didn't you?), there is one feature of Vista that Microsoft saw fit to take away and for the life of me, I can't understand why. They eliminated the Windows Sidebar. It was incredibly useful to me. I used it to place the Calendar, Clock, Weatherbug and CPU/Memory usage meters where I could always see them while I worked. Windows 7 still supports gadgets, but they can't be docked on the Sidebar any more and if you want to have them visible, i.e. on-top all the time, they sit on top of your work. I like to work in full screen mode for most of the programs I use. With the Vista Sidebar, you could set that to be always on top and when you launched Word, for example, it automatically opened to fill the entire screen to the sidebar. Now it is necessary to manually resize the application window to avoid having it either cover the gadgets, or else the gadgets very annoyingly sit on top of the application window, frequently covering parts of the ribbon menus.
Microsoft, if you see this, can I please have my sidebar back?