Seems like a much better solution than trusting the Posterous founders not to mistreat their users again. They recently posted their new site trying to get $5/month out of people losing their content on their old site, lol.

Great timing. Images etc in the posts are moved too? Can I choose a theme during migration?

If you have post with one Image its moved to Tumblr but for embedded images / media give us some time :)

Basically most of the users will have seamless move & for rest we are on it.

Great idea. Any similar services for wordpress?

There is a plugin for this currently. If there is good demand we can get it ready in few days with full media migration.