I would like to request a 2-page view (open-book-like) (or even 3-page... I use this in Word frequently) in the internal PDF viewer. It would help a lot in reading long scientific articles on large high-res screens.
For an idea that is a bit out there, but may be interesting for the upcoming dual-screen devices:
being able to show two non-sequential pages of a PDF (or even websites?) next to each other with independent scrolling would be great for browsing long papers when you want to see keep e.g. page 5 visible while you refer to some detail on page 26. This can be achieved by opening two independent windows, but keeping it all in one window would allow me to click internal PDF hyperlinks on the left-side panel and have the right-side panel move without manually changing the view of the document.