Make sure you have a business model which is profitable and if that includes advertising, so be it.
None of us want a repeat of what we have gone through with the Google Reader fiasco this past week. Google failed to capitalize on their system by not bothering to directly generate revenue from what they were doing. I am not convinced you can exist without a profitable business model so if that means you need to incorporate advertising on your pages, please do so. Advertising could certainly and easily be tuned to the type of feeds we are using so I see the potential as enormous. Given your now massive user base, the potential for income for you people is significant, so please do what is necessary to keep the Old Reader alive.