As someone of you already know, I'm an iPhone user from a month. One of the coolest feature of this device is certainly the App Store, the place where you can find any type of application you want. 
With the 2.0 software update (out for the iPhone 3G launch) Apple has placed the App Store feature directly into the device (no need to go on an Apple website).
Why the App Store is so interesting? Because now you have a central location where you can find all you need. The App Store permits you to browse for a software by directly searching the entire archive for keywords, by browsing different categories, by searching the Top 50 or the Top Downloaded.
Applications can be free of charge or under payment (normally a small fee). When you've found the application you need, just tap on it with your finger and it's downloaded to the phone via WiFi (if it's active) or via a cell network.
What is cool is that the App Store maintains your applications always update. If there's a new release available for an application that you've previously installed on your device, the App Store will automatically tell you that a new update is available and it permits you to automatically update your software "over the air". Installing or updating every type of application via App Store on the iPhone requires only a finger tap.
The App Store concept is interesting also under the hood. 
Apple certifies that application distributed via the App Store are 100% safe and compatible with your device. If you're a developer that wants to distribute an application via App Store, you've to pay an initial fee to be admitted and after the acceptance you're free to pick the application price (free or not). If your application is free, there's no charge for users and developers. If your application is not free, a developer gets 70% or the revenues monthly.
The App Store is the exclusive official way to distribute iPhone safe applications.
I think that this concept could be interesting also for Windows Mobile. Why not having a central repository where all "100% compatible" applications can be placed for distribution (free or not)?
If you need a Windows Mobile application, actually you need to search for it via a search engine, go on different websites (secure or not, it depends...) and download it (and hope that it works...). And if the application is not free of charge? You' ve to pay with your credit card on different websites instead of a central secure location.
I think that the App Store is a great idea that could be interesting also for Windows Mobile. If I have developed a mobile application that I want to share with the community for free, I can upload the installer not on my personal website for example, but on the Microsoft App Store (after registration and admittance). Then, everyone that wants my application can download it from the central location, maybe directly via their mobile device (Windows Mobile could include a native application exactly like the Apple App Store application installed on the iPhone, so no need to surf the web).
And if I want to gain something from my mobile application? I can decide the price, the a user that want to buy it could directly pay via the Microsoft App Store (central location for payments) and then Microsoft will pay me. So simple and more secure than pay different people on different websites.
I hope to see this idea also on the mobile Microsoft world... it's really useful for the end user but also useful for a developer I think.
P.S. Don't forget two simple things that makes the Apple App Store so used:
- Low cost for applications (lots are free and the most are between 2$ to 9$).
- Simplicity to install and update applications.