Go to 'Customize' for your tumblr site and click 'Services.' At the bottom is 'Automatically import my...'. Choices include Delicious, YouTube, Vimeo, etc and RSS. Support is definitely lacking though and documentation is virtually non-existant.

I see, thanks. It's a shame that they don't advertise those features better. It's a major point why i use soup.io.

Definitely. I even emailed support about it and the response was 'This is not supported' -- like they had never heard of it. Go figure.