We're still optimizing the performance of certain operations. There are definitely still a few rough edges, especially with analytical queries as you'd pointed out.
As far as basic operations (inserts, updates, retrieving documents etc.) are concerned, RethinkDB already has competitive performance and we hope to publish official benchmark results soon. As you know, good, comparable benchmarks aren't easy, and we're currently spending most of our time on improving RethinkDB rather than working on those. But they're definitely coming.
This is just a guess, but a query involving COUNT(*) might execute faster with PostgreSQL since it can use an index for making the count basically a constant-time operation, while RethinkDB doesn' currently support this. That is definitely a missing feature on our end.
If you get a chance, I'd be very happy to hear from you about the specific queries and the data you'd been testing, so we can look into those specific performance problems. My email is daniel at rethinkdb.com .