Is this still a useful request? Here's what I got on my MacBookPro (junk is just 'main', junk2 includes "boost/date_time/posix_time/posix_time.hpp")
DuoTwo:~ marshall$ time g++ -I /Marshall/Sources/boost/trunk junk.cpp
real 0m0.056s user 0m0.025s sys 0m0.023s
DuoTwo:~ marshall$ time g++ -I /Marshall/Sources/boost/trunk junk2.cpp
real 0m1.641s user 0m1.395s sys 0m0.228s