You can now withdraw asynchronous proposals
Did you send out an asynchrounous proposal before you meant to? No problem! You can now just withdraw it by clicking the little 'x' icon in the Proposal column on the My Tensions page. Look for the icon after the number of responses information for that proposal. This will withdraw the proposal and you can send it out again or bring it to a meeting when you are ready.
See this announcement for more on asynchronous proposals.