For a long time CouchDB listed BBC as one of its largest users — you can read more about it Enda Farrell’s talk about CouchDB at BBC and CouchDB case study. At QCon London 2011, Matthew Wall talked about Guardian.co.uk usage of MongoDB. InfoQ hasn’t published the video of the presentation yet, so here’s Graham Tackley’s slides:
SkillsMatter has also published Graham’s talk at MongoUK 2011.
I guess from 10gen’s perspective MongoDB and CouchDB are even in this space.