[topher-the-geek]

> Just so we're clear, data written to HDFS does not flow through the NameNode.

I wrote that poorly. You're right, file blocks do not flow through the NameNode, only metadata updates do. The issues occur when the clients' metadata operations saturate the node.

> This is the point where I point to the hundreds of companies

Indeed. Many companies have had great success with Hadoop. It's one of the reasons Hadoop sees such broad use. However, other users' mileage has varied.