You guys are talking about data design, but there is another good reason for an RDMS--it is a big abstraction layer so that you don't have to worry about things like memory paging and block IO. If you pick a NoSQL database, you better make sure they have given more than a little thought to such issues.

Another issue is governance. How much private data do we have, who has access to it and who has seen it? Act as if you don't care about such issues and you might have an army of auditors in your knickers.