Depending on the season and the locale, going shirtless can be very common at races, especially those in the 5km to 10km range. In some summer races in relatively informal settings, more than half the participants could turn out in shorts, shoes and bare chest or jogbra. Elsewhere, however, the shirtless contingent can be as small as two or three die-hards braving winter temps and the spectre of pneumonia. Still, weather permitting, the arguments in favour of going bare - salted throughout these posts - apply to a race as well.
There are many races these days where the rule is simply that the event number bib assigned you be positioned 'in the front', meaning it can be pinned to your shorts or jogbra. Even more conveniently, some organisers now issue electronic chips attached to your shoe that tag you as you cross the finishing line, so that bib position becomes less important. Timekeeping is a cinch, among other benefits - including making going shirtless even more fuss-free.
If you're thinking of going shirtless at a race, you'd probably best be already used to going bare-chested during your practice runs (though there is an argument that, since going shirtless can often boost your times, you might want to stick to a shirt during practice and then lose the top for an extra advantage come race day). Given that there will be a lot more people present than during your usual trots round the block, you might get the jitters. You might want to start off in an old vest that you wouldn't mind discarding, so that you can strip down once you've worked up a sweat (at which point, as has been pointed out, the urge to go bare should overcome any residual 'shyness'). Don't forget to pin your race number to your shorts, so as not to have to transfer it from your vest midway.
As a general rule on this blog, it has been suggested that being around other folks who are comfortable going shirtless can be a help. However, this is probably NOT a good idea in a race unless your times are pretty decent, since AS A RULE the shirtless contingent that typically collects at the front of the mass is made up of fast movers. You might have trouble keeping up and that psychic blow could make you feel rather foolish.
However, if you have a specific friend or running buddy - whose pace will be roughly equal to yours - convincing him or her to race with you is wise in any event. Faced with what will likely be a great mass of people, most of whom will be shirted, you can draw encouragement from each other if you are both converts to the shirtless cause.
May 2015: First up, though I still try to put up blog content whenever I can, it has been easier to more regularly visit the the Twitterverse. Follow me at @barethomas10 and let's keep the shirtless running flag flying. Of course, the blog still attracts very interesting comments, and good discussion. Keep it up.
Second, in the years since this venture launched, and as shirtless running among women has gone increasingly mainstream, the term "jogbra" has clearly declined in use. I will thus prefer "sportsbra" henceforth - as has already been the case on Twitter, and in recent posts here.
I continue to welcome guest posts (sent to firstname.lastname@example.org) on any related topic, including from those who would discourage stripping to the waist. I am myself of course a fervent convert to the joys of running bare. But let all voices be heard!