>If you'd point me to a resource to answering this question, I'd appreciate it.

Do you need a multi-threaded dll in ALL the cases, for any possible case?

A multi-threaded program (COM dll or whatever) must deal with synchronization (between threads) problems. A single threaded program is much simpler, so, it may be faster and smaller. And don't forget, the simpler something is, the less chances for bugs! :)

Vlad