Let's say I have foobar running with a playlist currently loaded. If I double click on a music file in a Windows folder to play it, foobar plays it by wiping out the current playlist. Is there a way I can prevent it from wiping out the loaded playlist? Perhaps make it open a new temporary playlist?

Preferences > Core > check the box labeled "Enqueue incoming files by default etc etc"

Here are two ways to solve it:

1) [Preferences] -> [Core] -> Enqueue incoming files by default....
Will enqueue in the current playlist (without clearing it)

2) [Preferences] -> [Core] -> Always send to playlist:
Will always send files you open this way to a specific playlist.

And last but not least: I'm slow....

Edit: Spelling

Awesome. You guys rock. I'm so glad to be rid of iTunes. Thanks!

I've been a fb2k user for almost 2 years, and I've noticed I only appreciate it more over time - nuances that I didn't notice, things I hadn't thought of, etc