As much as I love the new interface, that Photo Choosr or whatever it was called thing was what really got me to sit up and pay attention.
Ever since using Windows Live Photo Gallery (and that Photo Gallery thing that came with Vista before it), I get annoyed when I have to use an open file dialog or something in some application where I need to open a photo that's on my system somewhere. I have to remember where it is, what the file is called, etc. You can search, but it's not ideal.
I always wished there was a way to just replace the Open File dialog in, say, Paint.NET, with WLPG, so that I could just use the WLPG UI to find the image file I wish to open. And now it looks like that is actually becoming a feature. Can't wait to see what happens there.