I haven't looked too much at the new Live Services stuff announced at PDC from a developers point of view. However from a users point of view I love it.
I am now in the position where I have my main machine (a large laptop) which I use for developing and presenting, and my Netbook (asus eeepc) which i use for being mobile.
I am now experiencing the pain of having pictures, music, source code on one device but not another. I see the synchronization between devices offered by Live Services as the real solution, very cool stuff.
When I get back, I'm gonna give it a bash and try and have my various devices sync'd up.
As soon as I do that, I can guarantee, I will start developing against it :)