Update 2: A HSCALE benchmark finds HSCALE "adds a maximum overhead of about 0.24 ms per query (against a partitioned table)." Future releases promise much improved results.
Update: A new presentation at An Introduction to HSCALE.

After writing Skype Plans for PostgreSQL to Scale to 1 Billion Users, which shows how Skype smartly uses a proxy architecture for scaling, I'm now seeing MySQL Proxy articles all over the place. It's like those "get rich quick" books that say all you have to do is visualize a giraffe with a big yellow dot superimposed over it and by sympathetic magic giraffes will suddenly stampede into your life. Without realizing it I must have visualized transparent proxies smothered in yellow dots.

One of the brightest images is a wonderful series of articles by Peter Romianowski describing the evolution of their proxy architecture. Their application is an OLTP system executing 200 million transaction per month, tables with more than 1.5 billion rows, and a 600 GB total database size. They ran into a wall buying bigger boxes and wanted to move to a sharded architecture. The question for them was: how do you implement sharding?