That's always the trick, isn't it? To
be aware without
sounding like you're aware.

I have a tendency to over-enunciate if I'm not careful. There's also an odd little Canadian quirk that I'm MUCH more aware of now than I ever was before. Canadians can sometimes have a tendency to lift their voice in a question when there isn't a question in the text. I'm told this is a mannerism that makes Americans twitch.

I do my utmost not to do that in scripts.
I'm in total agreement with Lee. Sometimes - especially when auditioning at some place like Voices.com - it isn't possible to talk with the person asking for the audition before sending in the audition. In that case, I will usually do what he suggests and offer two readings - one with the contractions and one without.
This is a great thread - and it asks a lot of questions I had myself! Thanks for starting it, Jason!