One of them -- Kevin Ritter of Timeless Kitchen Design -- even sent a link to a kitchen he did that featured tin wall tiles and concrete countertops. Looks good, doesn't it? I've also experimented with staining concrete (your garage floor is a great place to experiment), and you can get some nice color tones -- copper is one of them.
I don't know what I'll end up doing, but concrete is definitely worth thinking about. It would add a nice industrial edge to my traditional cabinetry.