I have mentioned this before on the discuss side but repeat it here in case it is lost in the noise floor.
I believe that advertising as a source of revenue should be left on the table.
First not to do so is irresponsible and presumptuous of community desires.
Second it may occasionally be essential to survival.
I suggest it is coded in and implemented in ways that are flexible and configurable. Make it opt in and make it user tunable. Let the user decide how much of his details leak to the advertising algorithm. Adverts may have just the right job or wireless router to market to him that he is needing. I do not propose to design the business model to rely on such advertising but I would be happy to see adverts if I do not have to make a monthly payment to enjoy answering questions. Remember everyone in a community wants to help a community effort and if seeing a few ads is the only way that a user can help why should he be prevented from helping. There are people who live on under a US$ a day who cannot donate but can click through an advert occasionally in a show of support.
Secondly as a possible ongoing funding model have posts and communities sponsored by companies. The community can have a main sponsor and popular posts could be adopted by sponsors using a voting system. So a really flattering answer about Microsoft might get sponsorship from them if they choose to outbid the Linux foundation or private sponsors. These can be time limited depending on the amount or competitive pressure.
My real point here is to bake in as many possible means of automated and network sponsorship models as possible so distribute risk and prevent single points of pressure from outside.