Some more information about Origami has appeared on one of Microsoft's blogs.
I've seen it asked "Will Vista run well on the UPMC?"
The Vista requirements aren't out yet, but realistically if the units have the hardware specifications that Vista requires they should be able to run it. My group will be doing a fair amount of testing to see how Vista runs on the various devices over the upcoming months.
Is there any kind of special sleep mode where you will still be able to, for example, receive email notifications, get IM messages, or listen to music, while keeping the rest of the unit in some sort of power save mode?
Not yet, but technologies such as SideShow in Vista could conceivably be implemented in a way for UMPCs to get the advantage of some of this. The Samsung AVS Multimedia functionality offers some things such as media consumption as well.