So glad you like the idea, Gargoyle. I really think it's an interesting study, even though I doubt if the collected knowledge will actually be of any benefit. I have to confess that we have only managed to check the key of songs when we are watching movies at home. It happens like this:

Me: Quick, Hildebrand grab the guitar. Here's the note Hmmmmmmmmm.
Hildebrand: Hmmmmmm. Key of whatever. Just a minute I'll turn on the piano. Yep, key of whatever all right.

Nowadays we usually watch films on DVD or video and it's easy then. Good luck with the key spotting, Gargoyle. I'll be interested in your observations.
Cheers, Joy