Most users would be pissed off if Tumblr put ads a/ on their blogs (extremely pissed off), or b/ in their dashboard stream of Tumblr posts from followed blogs (really pissed off). We consider that our territory, because it is by us, for us.
On the other hand, the Tumblr tags area has a definitely different feel to it, and therefore I think people would be more accepting of Tumblr going more mercantile there. First of all, if I am looking at the stream of all posts tagged ‘Yahoo’ or ‘Tech’ I expect to see posts from strangers, people that I am not following. Therefore, the tag stream does not feel like a personal space, one defined by me. Following a tag is not like following a person, it’s like visiting a museum.
Second of all, a handful of the most followed tags are curated by Tumblr. In these cases, Tumblr has expended time and energy to contact and work with leading Tumblrs knowledgeable about ‘Architecture’ or ‘Movies’ or ‘Food’, and then handing over curatorial tools to that group to pull in the most interesting and insightful posts relative to the tag.
Placing even a fairly sizable chunk of those tag pages to ad space — especially if the editors were somehow involved in deciding that the ads were relevant to the topic — wouldn’t run against the grain, I think. Moreover, the ads themselves could be made to feel like Tumblr posts, too, like Tumblr Radar — selected posts of general interest — currently does.
Perhaps it’s so obvious that it can go unsaid, but clearly some camera company would be willing to pay a substantial sum of money to have tens of thousands of people daily see its offerings when they visit the Tumblr ‘Photography’ tag page. Likewise for the pages associated with ‘Cars’, ‘Weddings’, ‘Wine’, ‘Tattoos’, and ‘Russian Brides’. Ok, forget the ‘Russian Brides’, but the rest stays.
So the answer for Yahoo is tag stream advertising.
The best angle might be for companies to use the space as a mini curation. For example, IBM might rent the space on ‘Social Business’, and curate great content on that topic from around the world. This would actually be providing a great service, since Tumblr doesn’t have curation on that topic yet. It might actually help pull the community into Tumblr, just for the sake of accessing that content.
At any rate, given the near infinity of topics that are of interest to groups of people, and the ready-made, bottom-up nature of tags, Yahoo could be selling Tumblr participation in this way on tens of thousands of tag pages, and Tumblrs would feel like they are better off, not dissed.
On a completely unrelated topic, Tumblr Pro could have legs, too. For example, I would be willing to pay $5/month, let’s say, to be able to pull any RSS feed into my Tumblr stream, so that posts from friends’ non-Tumblr blogs would just show up. Or the Bits Blog from the NY Times, or dozens of others. Tumblr could make money collecting fees for the Financial Times, or other paywalled destinations. There are obviously other premier services that people would be willing to pay for, over and above this pull-to-read service.