[michaelbuckbee]

There are a number of sites/webapps that do this already. I think the fact that it is a standalone app is actually kind of refreshing and opens them up for things like inclusion in the Mac App store.

http://easel.io http://divshot.com http://jetstrap.com

All do this directly at:

http://www.bootstraphero.com/the-big-badass-list-of-twitter-...

There are a bunch of web apps that do aspects of this (button, form and theme builders).