See forum thread at http://forum.37signals.com/basecamp/forums/2/topics/5429 regarding getting clients and customers to “respond” to a message rather than starting a new message thread.

The logic of the following proposed fix already parallels 37s’ protocol for many pages that ask you to confirm an operation (w/large button) or cancel (w/small text link to beside large button)...

Proposed fix: http://elderforestpublishing.com/message_quandary.html