We're progressively rolling out the feature right now. It should be available to all of our users within the next 24 hours.
SkyDrive supports editing .sql files in the browser, but we don't yet have syntax highlighting or completion suggestions for SQL.
That's disappointing but I'm encouraged by your use of "not yet". I'll hope this comes soon.
Incidentally, Windows Azure allows publishing of websites from Dropbox. Given that SkyDrive now has an online code editor it would be nice if Windows Azure could publish from SkyDrive too. Maybe wander down the corridor to have a word with those folks and see what they can do!