You're no doubt wondering what the issues were; they come 20 minutes in, and were (paraphrased):
* At scale in production, adding a new node took days to complete all the handoffs; they recommend adding new nodes as soon as it's looking like you need them, rather than waiting until you're redlining.
* 2i is slow, especially in EC2; a straight KV "get" is milliseconds-denominated; 2i index queries were taking multiple seconds. Use 2i, they say, but in background processes.
* Javascript MapReduce is slow; this is well known. They confirm Erlang MR was adequate.
* As the LevelDB keyspace grows, there's a stepping function in latency; 5ms, then 15ms, then 25ms; the solution is to add nodes. (LevelDB is Google's KV store, a new option for Riak, required if you're using secondary indexes).
* Riak Control didn't work for them over low-latency connections.
* Once, a Chef misconfiguration left the whole cluster flapping on and off, which corrupted the cluster; they recovered with Basho support. Be careful about adding and removing nodes rapidly.
* Similarly, flapping a single node caused the cluster to get into a state where it wouldn't converge again; the cluster worked but no nodes could be added until they (presumably?) restarted it.