[Boost-users] When to use which functors?

I'm somewhat new to Boost, but pretty familiar with STL and Loki. I'm a bit puzzled by the wide array of similar-sounding libraries in Boost for dealing with function objects: Lambda, Function, Functional, and Bind/Mem_fn. Why are there so many of these libraries and under what circumstances would I want to choose one over the other? Thanks. - Bruce Johnston Simba Technologies