[boost] Which libs need multithreading?

I'm trying to package up a boost_1_33 RPM. The current default build produces single/multi thread variants of all libs. The current Redhat/Fedora rpm doesn't follow this. I'm tempted to just build single/multi thread variants of all libs just like the default build, but my question is, for which libs does multi-threading actually matter? Is there a subset of boost libs that actually change behavior with this switch? I'd like to get a minimal set.