How many Angels Dance on a Pin?

I was struck by the following statement.

"Philosophers may argue about how many angels can dance on the head of a pin, but scientists understand that there is no way to disprove any number of angels on a pin. "

http://www.synapses.co.uk/evolve/lec1b.html

Angels dancing on a pin has become kind of an idiom for useless debate. But I'm curious about where this phrase came from. Did the medievalists actually debate this? if so, what were the issues and arguments?

Anyway, while googling, I found two different answers attributed to the 13th century scholastic Thomas Aquinas.

http://www.straightdope.com/classics/a4_132.html

"Finally, he inquired whether several angels could be in the same place at once, which of course is the dancing-on-a-pin question less comically stated. (Tom's answer: no.)"

http://www.everything2.com/index.pl?node_id=523054

"In Aquinas' view, the correct answer was "infinitely many": while angels have no bodies and occupy no space, they do have location."

I can imagine a hundred angels doing the Snoopy dance.

http://youtube.com/watch?v=6-Ei-ZFttsQ

Reminds me of the joke of which I'll give you the paraphased and sanitized version.

It was a hard day. Boss lady screamed at me. I got a flat coming home from work. The kids were crying. In the mail was an invitation to an IRS audit. I settled into my easy chair in front of the TV and then suddenly the doorbell rang. Who should appear at the front door but the sweetest little angel holding a Christmas tree. She asked, "where would you like to put this tree?"

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