I'll agree they are not operational nightmares, but now that we're set up with Riak we can do things that I'm pretty sure your Postgres/MySQL/etc. setup cannot.
1. Add individual nodes to the cluster and have it automatically rebalance over the new nodes.
2. Have it function without intervention in the face of node failure and network partitions.
3. Query any node in the cluster for any data point (even if it doesn't have that data locally).
I'm sure there's other things I'm missing, but the point made by timdoug is the key one. We're at a scale now where it's worth trading up-front application code for reliability and stability down the line.
1. Add individual nodes to the cluster and have it automatically rebalance over the new nodes.
2. Have it function without intervention in the face of node failure and network partitions.
3. Query any node in the cluster for any data point (even if it doesn't have that data locally).
I'm sure there's other things I'm missing, but the point made by timdoug is the key one. We're at a scale now where it's worth trading up-front application code for reliability and stability down the line.