According to the announcement from MongoHQ:

We are still road-mapping our integration process, so it is important to note that there will be no immediate changes for our users. We are working closely with the users at MongoMachine to inform them of this as well. As we move forward, we will work with each of them, providing support and solutions that meet their needs.

We've seen surprisingly little in the NoSQL market so far this year. The biggest event was the merger of CouchOne and Membase to form Couchbase. Also, platform-as-a-service provider DotCloud acquired DuoStack. Both companies provided MongoDB (and other NoSQL) hosting as part of its service.