Carrying two cameras with lenses on vacation - your experience/advice needed

Photography is my heightened interest. I have aCanon Rebel XS which is just fine for my needs. But I find changing lenses a pain and that limits my photos. I have a 17-55mm 2.8 and a 50 mm 1.8. So I am thinking of buying a 60D for a second lens-always-mounted (with a 85 mm 1.8). This gives me more flexibility with portraits and detailed shots (that's where I believe the interest lies).

What I wanted to know is your experience in carry two cameras along on a vacation? I can justify the need for an event photography, but how cumbersome have you found carrying two cameras along slinging them over the shoulders. Over a period of time, I will retire the Rebel anyway. My camera bag is fairly heavy already with the body, the two lenses (17-55mm, 50mm), 3 ND filters, Polarizer cases, chargers - you know all that one needs on a trip.