I wonder if the increase in adverts is based on someone thinking that it will pay for their site's cost or if they're doing it with the mindset that advertising is their business model rather than providing interesting content.
The rule of thumb is pretty simple: If you're not paying them money then you couldn't possibly be their customer. You're probably actually their product.
In some cases - like GMail and other communications services where other people are involved - you and the people you communicate with are their product.
The "second hand smoke"-style effect of these "free" services has been largely ignored. Making a (bad) decision to trade your privacy for some service can be morally justifiable. Making that decision for the friends/family you communicate with is another thing entirely.