When I'm talking about 'bypasses', I'm talking about the official chicken runs, not just walking around the side (because as Stu said, the boardwalks are there because they're to avoid the gloopy sections of trail that never drain well.
But I was told that I shouldn't call them chicken runs, because they make manly men feel all unmanly.
Most of the bridges are really short, so if you do think they look a bit sketchy it'll take seconds to hop off the bike, push it across the bridge and get back on. Just make sure that if there's anyone behind that you let them pass first. They're generally fine in the wet though, as long as you take it easy. I've only come a cropper on the boardwalks twice:
* Once on the Stegosaur - the people in front had suddenly stopped, so I stopped. They set off, I let them get a bit of a headstart, went to set off... and somehow managed to shoot sideways. Bike went off to the left, I landed on the bridge in a slightly bemused fashion.
* Second one was the aforementioned accident on Aunt Flow, where I hit the rock step onto the bridge a bit iffily - I would have been fine with a bit more speed. I stopped, and put one foot down, but it was off the side of the bridge. I stood for a few moments, with one leg on the ground, and the other cocked over the bike, still on the bridge. Then I fell over, and slashed my leg as my bike landed on top of me. My pedals are sharp.
It's interesting to note that both of these incidents occurred when I was actually at a stop, rather than riding. I should also point out that I'm not terribly good at mountain biking.
It's all just a blur when I go round
I only pootle around at sloth-like speed so that I can give handy information! It's a dangerous job, but somebody has to do it!