Well one thing we store is HTML content and "MS Word" like document data. We also store hundreds of revisions for all of those documents. I wouldn't want to use

Well one thing we store is HTML content and "MS Word" like document data. We also store hundreds of revisions for all of those documents. I wouldn't want to use an RDMBS for this because (a) its not relational, but also (b) backup/replication/load distribution would be too painful. A system like CouchDB can be spread out over n-machines, any of them write-capable.