This sounds really great! This is a very important feature in the university environment, as has been noted. Even approximated page count is cool, because when somebody refers me to a page # it is certainly better to be few turns away than trying to calculate the possible position in those huge Amazon numbers
Two things I'd really love to see:
1. As already suggested, giving users the possibility of their own page markup would be great. Especially with extensively used study materials...
2. When converting from a OCRed/original PDF, could Calibre add page breaks (markup) to where it was in the PDF?