I think I will just summarize the comment I posted over on Woothemes here then! :)

In my opinion, Tumblr is more than just a quick way to post videos or pictures.

If you have used it, I am sure you have seen how it works for everyone: you follow and are followed, you check people's posts from your dashboard, and you reblog what you like with two clicks of your mouse. Once you start following more and more people, reblogging represents an important part of your blogs content: much like Twitter retweets in fact.

In the end you do not even check people's pages, you get everything in your dashboard.

So I do not really get why we compare WordPress and Tumblr, when Tumblr is actually much more Twitter-like.

Can you implement Social features, develop a community of followers and friends, display a dashboard with all their recent posts and the possibility to post quickly from there, all this with WordPress? I am sure you can do it, nothing is imopssible, but what is the point?