> If you are able to do this, it turns out that the global write lock really doesn't affect you. Blocking reads for a few nanoseconds while a write completes turns out to be a non-issue. (I have not measured this, but I suspect that the acquisition of the global write lock takes significantly longer than the actual write.)

Actually, it does affect you. I have worked with mongodb in production in a high-write scenario with about 1000 clients and it slowed to a crawl. All data was in memory. The server was not breaking much of a sweat. mongostat showed upwards of 60 queued reads/writes at any given time.

The only solution was to shard, but I feel like an enormous server like the one we were using should be able to handle 1000 writing clients.

Keep in mind this was version 1.8. I no longer work at the company where this happened and cannot testify to the performance of 2.0, but 1.8 has abysmal write performance.