Pinning these "immersive app-like experiences" to the task bar sounds like one step back in terms of UI innovation. Having different webpages available from the task bar looks exactly like what I had with IE6 and multiple windows.
If it's anything like Fluid.app [1] on the Mac then I'm a big fan.
I have numerous web-apps setup as dedicated applications using Fluid and find it much nicer than having them as tabs in the same browser, or in their own browser windows. It means I can launch them with Spotlight easily, they have their own icon in the dock and start up without the address-bar or any other chrome.
At any one time I'd say around 75% of the apps I'm running are Fluid.app instances.
