[defunkt]

Counter example: nginx, which uses fork(), and seems to smoke Apache while offering features like binary reloading without dropping connections (not sure if Apache supports this but I seem to remember no - please correct me if I'm wrong).

Portability is not always necessary - when talking about fork() and friends you're talking about trade offs.

When I'm only ever deploying to Unix environments, I accept the lack of portability in exchange for features I value.

[mrshoe]

That's not really a counter example. nginx does indeed fork off child processes, but it uses async I/O in each child process. It doesn't use the traditional pre-fork process-per-connection model that Apache's pre-fork MPM uses or that Unicorn is using.

[defunkt]

nginx relies heavily on system calls at the expense of portability.