I absolutely HATE that stage fright feeling I get when I'm about to launch new software into production mode for a client! Anyone else feel that? Makes me want to vomit thinking of all the promises I've made that it will work fine and then all the things I don't even realize could go wrong. I never have enough testing resources because client budgets tend to favor shiny features at the expense of testing.

*raises hand* I feel it. Usually I just try taking deep breaths and hope and pray nothing screws up.

One thing I've learned in school that always stayed with me was "Always undersell everything". You shouldn't run around telling people you code shit but a sentence or two at the coffee maker about that one feature that breaks randomly without explanation can easily lower their expectations. If it works fine no one will care, if it doesn't it will be expected. Also ask as much as possible, even if you don't need to it shows them that you were working on it so they will either assume that you are completely incompetent (you want to avoid that) or that it's just a hard thing to implement. Most clients aren't actively running around trying to be malicious, they just can't distinguish between easy and hard things to do in programming so you should give them a feeling for it.