@lem729, you make good points. But in my thinking, I tend to lump renting 'favored' placements in a browser (search engines, news feeds, etc) in my category 2. I believe such rented placements equate to somebody paying the software maker for the user data which indirectly derives from the use of such a feature (which is the only real way the placement-renter can derive tangible benefit from such placements).
I strongly doubt that click-count rebates by themselves can financially underwrite the cost any software product for very long... which is why so many "free" software products are being driven to find stronger revenue-raising methods, be they bundled tie-ins, ads, placements, or whatever.
In some ways, I think Opera stands closer to Microsoft and Apple in all this, in that they have long utilized their desktop browser product to enhance the positioning of their other, more-profitable products. Whereas, Google uses Chrome to enhance its main business of harvesting/marketing user data and Mozilla is trying to largely go it alone with mainly just a browser product.
I agree that the presence of ads devalues a product in many users' eyes... but that remains relevant only so long as they have effective alternative browsers without ads, an option which seems to be teetering on the edge of extinction. Conversely, there are also many users who simply don't care all that much about ads... a fact borne out by the nature of all kinds of print media, in which "users" seem to willingly accept far more ads than genuine content - even when they're paying for the product. I hesitate to describe this all as a "dumbing-down" or desensitizing of the user population regarding ads... but it does seem to be a direct consequence of cost realities resulting from the "free" software product paradigm.