1) Vista is slow.
2) The restore function never works when you need it.
3) It interferes with your work constantly with daily and often hourly security updates or other updates and with pop ups that freeze whatever is running to ask if you authorized an action when you obviously have or even if it is an OS program function
4) Stops all progress when it gets bogged down with who-knows-what - basically you don't want to run more than one slightly complex program at a time
5) Changing settings is a laborious process in which it is sometimes very difficult to find the settings in the first place, then it reverts back to factory settings anyway!
6) Media functions like the Windows Media Player or the Windows picture viewer never work right.
Windows 7, on the other hand, is the opposite.
1) Extremely fast
2) Easy to-get-used-to new interface
3) Looks great (aero styling actually works)
4) Restore works just like it should, always works and the need to use it doesn't come along very often either
5) Security issues or anything regarding maintenance is handled intelligently and only asks for your attention when your input is actually required
6) Buttons for things you need to get to quickly like updates, sound, usb plug ins and network settings are easy to find and quick to get to
What I don't like about 7 is that you can't change the way things behave as easily, such as going to the start button to bring up the menu - it stays in the pop-up box and doesn't expand like XP and you can even make Vista do. The options on the bottom bar are not as manageable and it merges an icon designed to open a program with the open window tab when the program is already running - this can be confusing until you learn to right click to open a separate instance of the same program and it's harder to get to the control panel (another right-click feature). Windows Media Player is still glitchy.
But overall, I am very satisfied with Windows 7 and feel a heck of a lot more secure too.