For SharePoint on Office 365, is there a way to show a "Page Last Updated MM/DD/YYY" chunk of text, where the date is programmatically generated?
Are you using Publishing pages or regular Web-Part/ Wiki pages?
For publishing is extremely easy by using the Publishing Fields in your page Layout targeting Version property and i use something like (just target Modified instead - however be aware that you have no control over the Date format - reason for which I've created a Calculated Column to display date nicely!):
For web part pages - directly in the page you would need to use may the so called "ProjectProperty" that comes with every list item (which includes Pages, Document, etc.) as such (Marc A. has detailed these http://sympmarc.com/2009/02/26/10065/), however i must confess i haven't used it for Version.