I have a friend whose primary bike is a custom Seven in titanium...she swaps out tires for road or off-road riding. My dream bike would be pretty much the same sort of concept, except with disc brakes (since the brakes commonly used on CX brakes don't stop well on the road from higher speeds). I'd have 2 sets of wheels--one mounted with slicks and 1 mounted with knobbies. It's a pipedream for now, but maybe in 3-5 years it would happen. It would be kinda cool to have one perfect bike.