Yesterday Google announced support for the same. And lucky for us, the same tag works for both MSN and Google:
Both have their own tags as well, but no need for those when there is One Tag To Rule Them All (well, after Yahoo! gets on board!)
Update: Search Engine Roundtable is posting a clarification they received from Google. Using this tag will block not only ODP descriptions but titles as well. Not only does Yahoo need to add support for NOODP, but NOYAHOO as well. Yahoo often uses titles from the Yahoo Directory in their search results. Would be nice to opt out of that as well.