If I'm racing a triathlon then no (putting on gloves takes time). Unless it is really cold, or a middle or long-distance race (I've only done a couple of these).
Otherwise; if I'm on my road or TT bikes and in lycra mode, then yes.
If I'm on my Brompton, then if it is cold I will wear gloves and if it is not then I won't (I'll be wearing what I'd wear to walk about). However I had a very minor off recently (too fast and a pothole) which left me with a grazed palm and since then I've been eyeing up a pair of "cycle-chic" style fingerless gloves for the summer...