We had this discussion in our writer group about not using contractions.
I am thinking this does not apply to comic books at least not in the dialog.
One People often verbalize using contractions.
Two Contractions take up less space in the dialog bubble.

Am I right or wrong in my thinking?

It's certainly A-OK for dialog. As for captions, you can use them if you want to, but most comics aren't narrated that way; it just depends on how you want to narrate, or how your character talks in his/her head. Panel descriptions...I'm not sure about.

Yeah...there are no hard and fast rules about contraction use. They are only as beneficial or detrimental as your style. Nothing more.

I don't really think that contractions should matter in any sort of dialogue. People speak using contractions, and the goal of dialogue is to accurately represent conversation. I think not using contractions in dialogue actually leads to clunky, unbelievable dialogue, unless you're writing a particularly stuffy or proper character.

Not using contractions is more of a NaNo thing, for which word count counts. For this, contraction away, because you should skip down a line anyway for each character's dialogue or whatever.

I don't know if this will even get seen, because we're so far away from Script Frenzy '10, but yeah, use contractions.

I've got experience writing comics, and working as an English and creative writing teacher, and believe me, nothing takes me out of a story more than wooden dialogue. Most people use contractions, so most characters should too, unless they were raised specifically not too (like a member of nobility).

As for in the script itself, I don't see why not. The narrative is your description to the artist (or film director, if that's your thing) of the action. You want it to be easy to read, to flow well and be exciting. And again, since most people use contractions, it might seem clunky not to use them.

Now if you're writing prose, or formal essays, you'll have to pick and choose, but I say yes, always, to it in dialogue.