Hey there...I am one of the founders of MongoHQ. We get this question often. I think that the issue is less about getting up and going with a technology (generally, that is the easy part), but the reality that it is something that you still have to manage as you get increasingly busy. So:

1) How are you going to handle monitoring?

2) Do you feel comfortable making the right moves when you are faced with growth?

3) Do you feel comfortable optimizing your database as things change?

4) Do you have time to stay up on all the updates to MongoDB and how they can affect you, what improvements are right for you, etc.? The space is very busy.

As part of both of our shared and dedicated offerings, we offer this to our customers and can assist them as they grow and their needs change. Hosting the data is the easy part...mastering the domain is what takes effort. We do our best to help our users in this way.

One final note...we do offer consulting, installation and monitoring of in-house MongoDB setups. That way, if you did want to run MongoDB on your own platform, we could assist you. I'd love to talk to you more about it if you would like. My email is jason@mongohq.com.