You answered your own question above, and also identified why app.net won't interest you. If you're okay with ads, then I think you'd get zero utility from app.net
Are ads in and of themselves really a huge problem? I don't find myself often annoyed by them. Now if there were a systemic change to the service because you didn't have to alter the experience for users to generate ad revenue, then I begin to understand. However if this is the idea, then in what ways the service would be different is exactly what I'm trying to figure out.
Remember, there are two sides to the coin "we offer a better experience without the ads" method. First of all you are going to get a smaller user base. So how much are you going to charge? $5/month? $10/month? You would need to get a pretty massive user base to be able to pay the overhead and attract top engineering talent, so in the end I'm not sure you'd be a whole lot better off.
At facebook, they have engineers devoted to pleasing users, and others devoted to pleasing advertisers. It's a difficult line to walk, but it's a legitimate argument that advertisers may win in the end because Facebook is now a public company and must show positive earnings growth and all that.
App.net (I think) is proposing that if that line does not exist, they can focus 100% on building a product that users will love using, rather than something that strikes a balance between pleasing users and advertisers. I could see this being a better product in general.
All your concerns are valid though. I'm not on facebook myself, so this service itself has absolutely no appeal to me--however, I do think there are some good points behind the premise, and I've heard through the grapevine that a lot of people do use facebook pretty frequently.