I love talking on the long, flat low-traffic parts. My excercise-induced asthma is such that the relaxation of talking to someone does wonders to control my breathing and relax me before a hill. That said, I often get worked into a wheeze-fit such that my only communications involve nodding and thumbs up when worried co-riders ask, "are you okay?!"

Mountain-biking is a different story--I'm usually concentrating too hard on the singletrack to chat. However, I do narrate my ride with little yips and curses as I go over the unexpected or tricky bits. I also like a few wild, "WOOOOO!"s down big hills, and more than once I've let out a bewildered "HOW AM I STILL ALIVE?!"s after a particularly interesting obstacle.