I use ImageWell to submit screen shots of work to users several times a day. It has taken the extra pain of having to convert from .pdf to .jpg formats to send an image. I dig the fact that I can compose an email, and while still in the Mail.app, drag a .pdf file to the menu bar icon, then drag it out of the pop down window directly into my composed message.

I do agree with previous feedback that the UI needs some work to be more intuitive but otherwise it's a great app for a 1.0 with lot's of potential.