> For a webapp where you don't have any page reloads, the exsting google adsense is pretty useless.
You could just auto-refresh the javascript using an iframe if necessary. That would solve that problem at least, although it may raise some additional ones.
There are sites that do auto-refreshing with other ad networks. AdSense may forbid it, but they're not the only network. I'm certainly not suggesting it as a sneaky thing to do. Some webapps are opened for hours at a time (as the OP stated). Acting as if that multi-hour page view is equivalent to a regular page view and showing only a single ad is ridiculous.
Good idea, but you're not allowed to use adsense in an iframe, additionally it would not pick up any keywords from the surrounding page so it would likely stay on public service ads etc.
You had me worried there for a second but it turns out that you are allowed to display adsense in an iframe although google says -
'Our targeting technology is not optimized to serve ads within a separate IFRAME. If you placed the AdSense code in a separate IFRAME, your site may display less targeted ads or public service ads.'
You could just auto-refresh the javascript using an iframe if necessary. That would solve that problem at least, although it may raise some additional ones.