At AgFlow (<a href="http://www.agflow.com" rel="nofollow">http://www.agflow.com</a>), we've been using RethingDB for 2 years (since version 1.3 to 2.0). Eventually we migrated to PostgreSQL.
The query language from RethinkDB is very powerful. But it's nothing compared to SQL when it goes to expressiveness and performance (at least on PostgreSQL). ReQL is deceptive. It performs well as long as you don't embed JavaScript or don't do sophisticated joins (even based on indexes). When doing more complicated queries it becomes very ugly and slow.<p>Our main motivations for migration was:<p><pre><code> * transactions
* performance
* tool kits around SQL
</code></pre>
We are very happy after migration. Backup process is way faster.
I think there is only one place where RethinkDB is better then PostgreSQL: replication + automatic failover.
If your data is not in TB, then I wouldn't recommend Rethinkdb. World with relational DB, transactions, pl/sql, pub/sub, GiS, data constrains, stability... offered by PostgreSQL is way easier, reliable and offers better performance.