A nice call-to-action button is important for emails, and I think it should be easier to build and insert them while designing an email. Some other marketing automation tools have it, and there are other sites out there that do this:
http://www.cssbuttongenerator.com/
http://css-tricks.com/examples/ButtonMaker/
http://css3buttongenerator.com/
Seems like an easy win. Whatya say?