Pure Genius Or Pure Stupidity: Does An Old Mac G5 Make A Great BBQ?
Personally, I would lean against this for several reasons:


The aluminum used in the Mac Pro cases isn't food grade metal.
Some of the adhesives in the case were potentially noxious.


I realize it's tongue in cheek, but keep safe, people. :)

Edit:

The frame of the Mac Pro(s) are basically aluminum. So you can take it to your local metal recycler and have it scraped for aluminum in exchange for money.

You can also refer to Apple's recycling policies.

Ebay/Craigslist are other options, as there are system rebuilders who would love to make use of an old Mac Pro case.