There are responsive design available in UnBounce which I expected.. The UI seems ok though.
No doubt that Unbounce is an excellent landing page builder but it is very very expensive :(
The Good News is, I finally ended up with a great alternative. It's called FrontMeter.com; they charge $97/one time fee and has a ton of features including the ProScanner feature that allows you to copy any page design by just entering its URL.
I hope you will also find this tool very useful :)
Our users have written 2 comments and reviews about Unbounce, and it has gotten 8 likes