Sumatra PDF 1.5 released on Apr 23, 2011, and includes more important features,

• add support for viewing XPS documents
• add support for viewing CBZ and CBR comic books
• add File/Save Shortcut menu item to create shortcuts to a specific place in a document
• add context menu for copying text, link addresses and comments. In browser plugin it also adds saving and printing commands
• add folder browsing (Ctrl+Shift+Right opens next PDF document in the current folder, Ctrl+Shift+Left opens previous document)

btw,
Last week, I noticed MuPDF trunk adds XPS support, but still has some bugs in windows registers.