The thing is. I actually like the GUI part of Evolution. mutt just looks damn ugly. I use it to read LKML but that's it. I place reading email up there with web browsing, and I personally think they both do better with a GUI interface than plain text.
I like to have a preview screen. I move mail all the time by dragging a message over to a folder with the mouse. I do wish Evolution had better keyboard short cuts, as I probably could move messages faster with typing. I did with alpine. But mutt still seems hackish to me, and I never got past it. I've been using it for LKML for a few years now, and I still don't care much for it.
Evolution is big and slow, and I need to kill it as often as I do my browsers, but other than that, it works well for me. If it had better key bindings, I would dare call it an awesome application.