I've had a couple of people come up and ask why they should be using the Windows 7 beta so I thought that I would list a few of the reasons that I've been giving.
1. New Taskbar
The new taskbar has been written about extensively so I'm not sure there's reason or me to elaborate about it functionally.
The great thing about the taskbar is what it allows Microsoft to do long term with the concept of windows, documents and applications. No longer do applications have to solely exist within their windowed environment, but now there's a great launching point for quick, common actions that users want their applications to perform. Additionally, I'm really excited to see the current MDI fad go the way of the platypus*. MDI implementations have been mostly driven in the browser sphere basically because Windows used to suck at managing a whole bunch of windows belonging to an application. Windows 7 fixes this and blurs the distinction between an MDI and SDI app to the point where "tabbed browsing" is no longer a feature people need.
* Within the software industry there seems to be these pendulums that keep swinging back and forth. We've seen three major swings of the distributed vs. centralized within the last ~50 years: the rise of the mainframe (centralized) which gave way to PCs (decentralized) to where we're at now which is Web 2.0 type of centralization. Eventually we'll get to a point where cloud computing is pervasive and we'll be decentralized again trying to get a bunch of devices working together nicely.
2. Window Management and Control
Windows 7 borrows from an idea that's been around for a while in MDI applications such as Visual Studio where you can "snap" certain display elements to the side of the interface. What this practically means is that if you drag Word to the left edge of the screen it "snaps" there and takes up half the screen. And if you were to drag Excel to the right edge it would snap there and take up the other half of the screen. And now you're super productive because you can see your Word report and your Excel spreadsheet at the same time without having to futz around with window sizes. That's awesome.
There are a couple of other nice improvements as well. Drag a window to the top and it maximizes. Sweet. If you use multi monitors you'll appreciate this: drag a maximized window from one monitor without having to un-maximize it and then drag it.
3. UAC Improvements
User Account Control was the controversial feature in Windows Vista. To put it plainly, they've made the Windows 7 UAC what Vista should have been. 95%+ of the complaints I got regarding UAC with Vista was that it constantly asked you if you were sure that you wanted to do an action that you initiated yourself. Examples of this might be changing the workgroup or various display settings.
Windows 7 has improved UAC to the point where it knows whether the user is initiating an action or some software piece is trying to initiate the action. By default UAC will only warn you of things that software is trying to do. This is a tremendous reduction of prompts and I'm sure the public will have a better reception to the smarter Windows 7 UAC.
4. Driver Support
No major subsystems have been rewritten for Windows 7 unlike Vista where several huge systems were redone and broke driver compatibility (video, audio, networking). This means that if your PC can run Windows Vista it can run Windows 7 for the most part. On the two machines I've installed Windows 7 on all drivers but one have been successfully installed. A quick trip to the Dell support site provided a driver for the last piece of hardware.
5. Improved Battery Life
I installed Windows 7 on my girlfriend's laptop and her battery life went from about five and a half hours to just under eight. That's a huge improvement for every laptop out there!
6. QAM with Media Center
QAM is a technology to deliver HD video over a standard cable connection provided by a service like Comcast or Time Warner. With the Windows 7 Media Center you can decode this and get picture perfect HD TV for free with a standard cable package and no set top box. Previously you would have to use something like Over the Air HD which had major pitfalls for people in downtown areas or in bad geographic areas. Grab yourself a cheap TV tuner and turn your computer into a Tivo.
7. It Works Better on the Same Hardware
Windows 7 performs equally or better than Vista in most cases on the same hardware. Netbook support for Windows 7 I'm told is a particularly compelling story. Ultimately the point is that you have almost no reason to fear the Windows 7 better on any hardware that runs Windows Vista. In some cases you'll find that it runs better than Vista ever did and that's a great success story. So really there's no excuse to not jump in.