[gominoa]

I left Pandora Slim playing for 18 hours straight with no interruptions. Just stopped it with 846 files created.

Nice! Glad to hear it!

Any idea how often the links to these songs get changed by Pandora?

If you're talking about streaming only, they seem to expire an hour or so after requested.
But the filenames in the cache folder are Pandora's songID and I haven't seen one change.

Also, I am saving to a folder in my Dropbox

Awesome idea. If Pandora Slim finds the song in your library it will play from there instead of redownloading