sincos

I think Dave Mayer got it pretty much spot on. You should use some sense and I wouldn't race a crit or go bombing down the Poggio like Sean Kelly, but a properly treated wheel and spare will have a lot of residual stick and you don't have to treat it like you're on ice. I've ridden dozens of miles on a spare more than once, in the hills, at a pretty good (but not max) pace. My issue with sewups is that they're a right PITA to repair. But swapping out a tire on the road is much quicker and easier than swapping out a tube on a clincher. These days I like more volume and lower pressure so I'm a convert to tubeless, but if your thing is skinny tires at high pressure, you could do a lot worse than tubulars.