CPM Advertising Questions…

Figured I’d make 2 separate posts since I wanted information on CPC and CPM advertising, obviously this is the CPM post Any information at all to a new comer would be greatly appreciated!
Can you run CPM add’s across multiple Sub Domains for different sites?
Will there be certain times where they limit how many impressions count towards one viewer?
Can CPM’s be run on Forums or will it count as just one viewing per viewer no matter how many pages they access if the banner is reloaded every forum page they click on?
And if there could be such a definitive answer, what are some of the highest paying networks for hosting CPM advertisements?

See original post by Jonny Reload