"""My position on mongo is thus: Its goal is humongous data sets, hence the name. Until well proven, I'm not the type to use it for huge data, but will keep an eye out for case studies."""

Actually Mongo is bad for really humongous data sets.

It works well if the working data set (the data you commonly need) can fit in memory.

Of course this doesn't scale very well with say several terabytes of data, while there are Oracle databases that handle a lot more...

In the case you Mongo you go to sharding etc and things get complicated in your app handling.