Stair porn is another great example of how to use Tumblr to the best effect; for example, I have one on Love Will Tear Us Apart.
StairPorn.org features nothing but stairs. I am sure some people do probably get off on this, but I would be fairly certain this site is aimed at architecture geeks and fans.
We have rabbits, skulls and now stairs. I am going to start a Tumblr for lettuce for the sheer hell of it. Rock on!