Hacker News is a very specific community and so by no means is this poll representative of the entire software engineering community, but I am so proud to see Mongo up there as the top non-sql datastore.
MongoDB has recently added a couple of new features, including sharding and auto-sharding. The growing popularity of Mongo among startups, its comprehensive feature set, and the flexibility of a no-sql data model is turning out to be a powerful combination.
If you are frustrated with your sql datastore and want to try a non-sql approach or if you are starting from scratch and want to try a modern datastore, please check out Mongo. You won't be alone.