XPS versus PDF

I just downloaded the XPS package from Microsoft download centre (Download page). This is a new format to compete with Adobe's PDF for electronic documentations. XPS stands for XML Paper Specification.

My experience:
XPS is really cool and keeps the final electronic copy very much like the original. It also seems to be designed as a modern alternative with ease of sharing, printing and archiving in mind.
However, the compression rate is a lot worse. Comparably, XPS of an elaborate two-page word document was 2 times bigger than PDF of the same file, and XPS of a technical article in Framemaker turned out to be 4 times of its PDF.
Also the XPS viewer looks nicer and easier to navigate and zoom in or out, but it is like a turtle when it comes to scrolling down a page.

I am going to just keep it installed, in case I need to view a document of this type. For now though, I stick to PDF.