The new user interface in Windows 8 is built around applications that do not run on the traditional desktop. Microsoft intends for their customers to use these new apps as the primary focus of their computing life, and to be able to do this on a wide variety of hardware. Allowing continued use of the desktop was a necessity in this "bridge" operating system, but clearly, Microsoft sees the new UI as the future of computer use.
This change from a relatively open desktop computing experience to one in a controlled, closed garden is a huge step, one that needs to be emphasized in its importance. Microsoft has complete control over what is offered to you in the Microsoft Store. And this store is the only source for applications to run in the new "Metro" UI.
I was looking through the Terms of Service that you must agree to when purchasing, or even downloading a free app from their store. There are some disturbing items in there. First off, you must sign up for a Microsoft account to get anything from the store. And this account must be used regularly to remain viable. If you do not use your account within one year, it can be deactivated, with ill effects on getting updates to any software you may have purchased.
The next thing that jumps out at me in the service terms is the limited nature of your purchases. You are buying a license to use the software, and may only install it on 5 devices at a time (as a general rule). If you try to install it on more, one or more of the installations will be removed automatically. Now, this isn't too different from software eula's we've seen in the past, where you are limited in the number of installations, but having one removed involuntarily and randomly is something new.
Up next is data collection by Microsoft. They reserve the right to collect information when you use the store. To quote the terms, "we may collect certain information about service performance, your service use and your use of your Windows 8 system. ... The Windows 8 system means the device running Windows, any software on that device and any devices or software communicating with that device." (Emphasis mine) They also state that they will share this information:
We use the information collected to enable the features you're using or provide the services you request. We also use it to improve our products and services. In order to help provide our services, we occasionally provide information to other companies that work on our behalf. Only companies who have a business need to use the information are provided access to them. These companies are required to keep this information confidential and are prohibited from using it for any other purpose.
Now comes one of the more disturbing parts. Microsoft can remove apps for any reason, and not only from the store, but from whichever device you have installed them. If you have purchased such an app and have it removed, they may reimburse you for the original price you paid for the program. If you have any data stored in the app and it is deleted, Microsoft says they are not responsible for this data loss. It is your responsibility to back up any data.
And of course, Microsoft reserves the right to change the Terms of Service at any time, for any reason. If you do not agree to said changes at a future date, your access to the store can be shut off.
Lets sit back and think about this change in the software environment for a bit. You're buying and using software that can be revoked involuntarily. This may not be a common event in the future, but it is a profound difference from what we've seen in home computers over the last 30 years.
My advice is to be very careful what apps you buy from the Microsoft Store. I personally will use Windows 8 from the desktop the vast majority of the time.