I think that's part of the fun! As long as they're close to the same size (to
ensure even baking). I've been recently liberated from the "everything must match" business.
I've developed a fetish for silverware...trolling through thrift shops and Goodwill for silver that has funky patterned handles, etc. I love digging through the boxes and thinking about the stories and all the dinners...My favorite pieces have a bit of history--old monograms, engravings (I have a knife engraved with the US Navy logo) and defunct airline pieces (definitely first class...).
Silverware has now migrated to cups, platters, bowls, and glassware. I've got several dinner parties planned after the first of the year for 20 or more people. I'm outfitting everything from thrift stores. In fact, I just picked up an assortment of 30+ old fashioned stemwear pieces--mostly the wide champagne glasses. Those I'll use for dessert vessels.
So use those mismatched coffee cups! It's the ultimate in repurpose and sustainability. smileys/smile.gif