Some helpful comments from @mikeal on a probable strategy for supporting domains. This would help, from what I understand, in two situations:

1. Putting exceptions thrown by .done() into the current domain.
2. When an event emitter or other domain-using callback library is used inside a fulfillment or rejection handler, and throws an error, it would escape Q but wouldn't escape the domain. E.g.

return Q.resolve().then(function () {
    doSomethingAsyncWithoutPromises(function (err, whatever) {
        // Q doesn't catch this, but domains would if we wired it up right.
        callANonexistantFunction();
    });
});