We were very well aware of its characteristics when choosing our DB, and didn't go in expecting any magic Web Scale or somehow getting a HA setup with plenty of durability with just one server.
For a multitenant CMS where you want to store documents with custom schemas, need more than just a key/value store and want some capability to do ad-hoc queries against custom fields, MongoDB is a pretty good fit.
We use mongodb for the analytics as well yes. It's a less obvious choice there than for the CMS part, but it's a good enough fit, in-place updates can be really handy and we prefer not having 2 different databases.
We don't index custom fields and for queries where that would be required we do the actual querying with ElasticSearch, but for simple filters on a custom field or the like, Mongo does fine.