Check out this concept video for Longhorn, the official codename for Windows Vista and Windows Server 2008. There's a mini-history of Windows at the beginning, showing the progression of Windows on the desktop as well as some of the innovations and hysteria that accompanied Windows 95. From there it launches into a quick demo about what the next version of Windows is supposed to look like.
What's most interesting is the fact that this video was created for PDC 2003, right in the midst of the coding furor for Longhorn. The video announces that Longhorn was coming in October 2003.
What this means more than anything else was the fact that those effects were designed and planned for equipment that was available in the 2003 - 2004 time frame. Dual-core processors, which are nearly mandatory for running Windows Vista today, weren't introduced until 2005. Also, in order to get the Aero Glass effects in Vista today, you have to have a video card that runs DirectX 10 and at least 128Mb of graphics RAM with 256MB being preferable. Even as late as 2006, finding machines with that much power was difficult. Finally, as you know, you wouldn't want to go near Vista with less than 2GB of RAM, and this would have been unheard of in 2003 on a desktop-class machine.
It shows that Microsoft was and is capable of producing a really slick operating system that doesn't soak up gigabytes of RAM and multiple gigahertz of CPU. Instead of what was promised and implied in the video, we wind up with transparent titles on Glass and Flip3D. That certainly puts the Wow in Windows, doesn't it?
Microsoft has already released early versions of Windows 7. Based on what Vista looked like and how it performed in its early stages as seen here, there's really no reason to expect that Windows 7 is going to be nearly as great as they say it's going to be.