I know it's probably a bit naughty, but it would be nice for Stack Exchange to prevent the default actions from occurring for Ctrl+S and Cmd+S on its sites. Instead of opening the browser's save dialog box, those commands should submit the current post.
It's up to me to decide how I want to use a website. Same with opening a link in a Window, I decide my browsing habits. I know ctrl-s saves the page (or document) it's universally accepted. With questions having a regular auto-save...why is there a need?
If you're still convinced, ask a question over at UserExperience.SE and see what they say about replacing a well-known key shortcut with a different one.
I'm all for a hotkey to post an answer, but why on earth Ctrl+S?
Ctrl+Enter would make more sense and isn't used for anything right now.