After upgrading the posting date fields are no longer visible when publishing a page.
In 0.6.8, these fields were made invisible unless a certain config option is set.
To turn them on, from the console or inside an extension, run this:
Radiant::Config['page.edit.published_date?'] = true
For example, this is what you might see if running the command at the console:
script/console production Loading production environment (Rails 2.0.2) >> Radiant::Config['page.edit.published_date?'] = true => true >> quit
Don’t forget the “production” after “script/console”, otherwise you will end up changing the config option in the development environment, which is probably not what you want.