You can spot Zell in the cafeteria before his formal intro.
He's over-protective of his house and especially his bedroom.
Despite his street-punk appearance, he is actually quite studious. Zell is constantly telling Squall about the history of various towns and events.
He calls his mother "Ma." ...Okay, we all knew that... But it makes him sound like he's from Brooklyn. :D
In the FFVIII demo, he wears his normal clothes to Dollet, not his uniform. Squaresoft even took the time to create FMVs featuring him in this outfit, then changed them again for the home release.
There is no official Amano artwork of Zell.
Some people think Zell is the son of Cloud and Tifa. FF games don't have a continuous timeline, so I can't say I agree... (His hair looks more like Cid's, anyway.)
In the demo, Zell's cussing was censored. (Our virgin ears!)