how much broadband usage does downloading the illustrator CC trial use up?

alrographics,

Presumably non critical, being more a question of download time depending on what you have available.

But you can ask in this specialized forum:

http://forums.adobe.com/community/download_install_setup

Roughly 1 - 1.2GB.

I find it rather shameful Adobe doesn't list the downlaod size of each app somewhere.