Setting Preview Default to Single Page

In Mountain Lion, at least, there's a Opening for the first time entry in the PDF pane in Preferences, where you can select Single Page. This sets the default view mode for all PDF files.

If you for some reason can't get it to work, you could try this Terminal command (don't know if it will work in Lion) and restart Preview:

defaults write -app preview kPVPDFDefaultPageViewModeOption -int 1

(in ML, the value of kPVPDFDefaultPageViewModeOption changes to 1 in Preview's plist, when selecting Single Page)

This terminal command should solve it

defaults write com.apple.Preview PVPDFDisplayMode 1

PS. This won't work in ML only in Lion. And you may have to restart before it will become functional.