Feature requested by @beyang.
Instead of Ctrl+Enter, what do you think of Tab, Enter?
I think Tab, Enter is more discoverable, less magical, and easier to know it'll do the right thing (you can press Tab, see that the focus is on top of Comment button, so pressing Enter is predictable). Ctrl+Enter could mean new line or submit, which is scary.
Talked with @beyang, he's convinced and satisfied with Tab, Enter solution.
Marking as resolved.