Is it production ready? I think so. The fundamental stream operators are in place. A comprehensive test suite checks out. Riemann has never crashed. Its performance characteristics should be suitable for a broad range of scales and applications.
There is a possible memory leak, on the order of 1% per day in our production setup. I can't replicate it under a variety of stress tests. It's not clear to me whether this is legitimate state information (i.e. an increase in tracked data), GC/malloc implementations being greedy, or an actual memory leak. Profiling and understanding this is my top priority for Riemann. If this happens to you, restarting the daemon every few weeks should not be prohibitive; it takes about five seconds to reload. Should you encounter this issue, please drop me a line with your configuration; it may help me identify the cause.
The Riemann talk tonight at Boundary is sold out, but I may deliver another in the next month or so. Thanks for your interest, suggestions, and patches. I hope you enjoy Riemann. :)