Suppose you have a bunch of computations, which you want to execute using [`foreach`](http://cran.r-project.org/web/packages/foreach/index.html). Perhaps you want to parallelize them, now or in the future. Each computation returns a single number. What is the best idiom to obtain the mean of all the numbers computed in this fashion?

I have two solutions in mind, which I'll post as possible answers so that you can vote and comment on these individually, and perhaps even edit them to improve them. But I guess there might be even better ways, so additional answers are welcome. My answers will include examples which you can adopt to demonstrate your own techniques.