Overview: Great way to run Windows on my MacBook Air (mid-2011), as well as my Mac Mini at work. Complete integration means I can move files between platforms, open Windows applications from OS X (Mountain Lion in my case) and vice versa. I can set application preferences for file types across platforms. And you can run Windows in its own Window or integrate it into the Mac workspace. Installation was very easy, no problems at all. Highly recommended. I wrote a detailed review below in case you would like more details on the features.
Update 3: Still going strong! I recently installed a sophisticated chemical engineering process simulator on the Windows partition, and it ran without a hitch. In facts, it was running faster on my 2-yr old MBA via Parallels than it was on some of my colleagues' newer Dells and HPs.
Update 2: The latest 9/6/12 update to P8 seems to have fixed most of the dual monitor bugs. One remains... if you closed down P8 in full screen dual monitor mode, the next time you open P8, the Win 7 screens are still on different desktops. To fix this, I simply exit Full Screen mode, and then re-enable it. Both Win 7 screens now show up in Desktop 2.
I have been using Parallels for over a week now (bought it early as a current user of Parallels 7. First, I have to say that Parallels has worked great for me. I use it at work, where it is a Windows environment. Parallels allows me to have complete access to my company's network and printers. Note, however, that this is all done by Parallels working through the Mac. So in order to see a printer or your network drives in Windows, you must have them set up in your Mac environment first. The Windows network environment mirrors that of the Mac. You can make you network drives show up automatically by dragging the network drive from the side pane in Finder to your Login Items list under Preferences>Users&Groups>Login Items. This is a great way to automatically log in to your drives every time you boot up.
The level of access between your Mac and Windows environment is totally configurable. For example, I can open a Lotus Notes email in the Windows environment, and select to open attachments (such as Word, Excel, etc.) in the Windows or the Mac versions of those programs. I can choose to share all of my Mac user folders windows, or not. And I can move files between Mac and Windows folders. You can also choose to totally isolate your Mac computer from Windows, but you loose network, internet, and printer connectivity.
Parallels has different view modes which are well-designed and seamless. Full screen mode takes advantage of Mac OS X's Desktop feature. In this mode, Windows is one of your desktops. It supports dual displays as well, which is a great feature. You can fully immerse yourself in Windows in this mode. You access the Parallels tool bar by moving the mouse to the top of the screen, and you access the Mac dock by swiping to the Mac window. My other favorite mode is Coherence, where Windows programs at just like Mac. When open, the program's icon is in the dock, and you access the Windows at the top of the screen and can be accessed from the Parallels icon in the dock.
What about performance? I have found that Parallels does not slow down my Mac. Windows performance is very snappy overall, but can tend to get the fan on my MacBook Air (mid 2011) cranking pretty hard sometimes. Parallels allows you to configure how system resources are shared, so you can optimize the Mac or the Windows environment. As for Parallels 8 specifically, they advertise that Windows runs faster than it did on Parallels 7. My experience has been the opposite. Windows for me boots up just a touch slower and programs are a little less responsive. Parallels 8 also adds multi-gesture support, but the gesturing, while responsive and immediate in my Mac environment, is very laggy (to the point of being unusable for me) in the Windows environment. Scrolling in Parallels 8 is also more choppy than it was in Parallels 7. However, overall, P8 feels more integrated with Mac than ever.
There are a couple of new/improved features I do like, but there is not a whole lot of them. One is being able to re-launch a web page from within Safari using Internet Explorer. Parallels puts an IE button in the Safari menu bar for easy access to IE. This is helpful when a web site renders best in IE. I can also now have IE in my Mac doc in order to launch it more easily. Windows notifications are now included in the Mac Notification Center. This is an okay feature, but Windows has been notorious about polluting my clean Mac notifications with an overabundance of Windows notices.
In summary, Parallels is a great program for those who want to be able to easily and seamlessly use Windows on their Mac. With more and more people bringing their own Macs to work and need access to Windows programs, Parallels is an absolutely proven solution. I use it every day at work with a dual monitor setup, and I am easily swiping between windows and Mac apps, sharing folders, and printing form both all day. Overall, I think P7 runs faster and more smoothly, but P8 is proving to be very capable as well. Plus, P8 is necessary of you plan to be an early adopter of Windows 8.