In .NET, you have WinForms and WebForms. The development model for both is exactly the same. They both offer several different controls you can use and provide an event driven programming environment.
Right now, with WebForms you have complete separation of UI and code. UI is html and server controls, while code is in a "code behind" page which can be written in any language.
There is not as much clear separation with WinForms. The UI is also code. But if you follow good programming practice, the separation can be made easily. With Longhorn and XAML, they are moving towards total separation. UI = XAML, Code = Any language.
Yeah, Microsoft is discontinuing a standalone version of IE. I think this is pretty dumb. They should continue to offer a non-Longhorn IE as they continue to improve it. They are betting on rich client apps in a big way. With .NET they have come up with a way to deliver these apps like web apps. You download a basic skeleton of an application. As and when, you need certain functionality, it gets downloaded and run dynamically. They have made significant improvements in deployment. You can just copy an application from one folder to another (XCOPY) and it will just run. No messing with registry, no worrying about DLL hell etc... These improvements are great, but I still feel they need to release new IE versions for pre Longhorn Windows.
Having said all that... I haven't seen many web apps use Flash at all. Yeah, they use it for animation, btu that's all. All "serious" web applications still make use of the web standards. It would actually feel quite wierd to use Flash apps. We are so used to seeing HTML forms and expecting certain behavior from them. I think, not a lot of people have taken Flash to be a serious development platform. It is still very much associated with the graphics/animation aspect. What do you think?
I have no idea about p2p. I have heard about the jxta sun project. I don't think Microsoft has made any noise regarding this. They mentioned something about having p2p capabilities in Longhorn, but that's it.