Tumblr absolutely does not do this.

Oops, so sorry to Tumblr. This was a reckless comment and I'm in the wrong here. I misheard from a good friend that Tumblr does do this, he was actually referring to a number of services.

Just received an email from Tumblr explicitly saying they don't. If I could delete the comment I would (but HN doesn't allow that), but I'll let this stand as my mistake and I'll back out from the Eastside-Westside tech battle.