Trying out tumbler, could it replace Twitter?

Woothemes recently blogged about creating Tumblr templates. I have purchased wordpress themes from them and have been inspired by there quality and custom support. I want to give Tumblr a whirl to see why the Woo team sees value in developing for this platform.

My reaction to the post is below -

I think its awesome you are exploring new platforms. I don’t have a Tumblr account, so this might be a stupid question – do you own the data you post to your account? I know the site says you can use your own domain, but this is much different than hosting it yourself. Does Tumblr allow you to export your posts? What if the service were to start charging for accounts or go under? What would happen to all your data?
Beside the functionality, ease of use and customization abilities, I love Wordpress because you host the site yourself and own all the data.

What do you think?