I work at Mint. We do use a lot of open source, but as others in this thread have pointed out, we only need to open source our code if we distributed modified GPL-like code (which we don't).

The Wesabe code is completely unrelated. We heavily use MySQL, Hibernate, Spring, XMLC and YUI.

We have contributed code back to the community in some cases, such as YUI.

If you want your JavaScript to be more Minty, I suggest you take a look at Matt Snider's excellent blog (http://www.mattsnider.com). He has code samples that are very similar or identical to what is actually in the Mint codebase. He explains the rationale behind a lot of the design decisions and to my knowledge, it's free for anyone to use.