After skipping Windows Vista on my main PC for it's entire life cycle, I played with Windows 7 during it's RC phase, and was instantly impressed. Installation was as easy as Vista (both are huge steps up from XP) and installation over a flash drive (takes some tweaking) is actually FASTER than Windows XP or Vista ever was. Features brought over from Vista, such as desktop gadgets and start-button search are immeasurable in how much use they receive. The GUI is much cleaner and easier to use, the start-button search is incredibly faster and more accurate than Vista's was, and the Aero Snap feature for someone, such as myself, running two monitors makes it easier than ever to manage multiple applications.
Driver support in Windows 7 is lightyears ahead of Windows XP or Vista. Most hardware doesn't require it's factory driver disk, or drivers downloaded from the internet, as Windows 7 will find them and download necessary drivers for you automatically. Getting connected to your network in XP or Vista was always a hassle if you didn't have drivers on-hand, as you'd need a second machine in order to get internet access, find, download, and transfer drivers. With Windows 7, you just turn it on and it works.
Windows XP virtual-machine is an amazing bonus, as well.
Windows 7's built-in remote desktop client is also very smooth and extremely easy to use, and is incredibly useful for controlling my old XP machine-turned-file server, as I don't need any I/O devices connected to it other than power and a network cable.
After using Windows 7 Professional since it's release, I cannot function NEARLY as well on any other OS platform. Windows 7 is the standard. It's modern, sleek, looks great, very customizable, extremely powerful, and is, in my opinion, the best Microsoft product ever created.