Every year 10,000 tons of steel goes into making paper clips
A few years back, undoubtedly during a slowdown in the economy, Lloyd's Bank of London decided to attempt to solve the paper clip paradox. It tracked a batch of 100,000 paper clips within its bank. Here is what it found: 25,000 were simply lost "in the shuffle," swept up or vacuumed into oblivion; 19,413 served as card game chips; 14,163 were twisted and made useless during phone conversations; 7,200 were used as hooks for belts, suspenders or bras; 5,434 were used to pick teeth or scratch ears; 5,308 were used as nail cleaners; 3,196 were used as pipe cleaners.
The remaining 20,286, or about 20%, were used for their intended purpose of clipping papers together.
Concurrency made simple introduces Doug Lea's util.concurrent package, which includes must-haves like work queues and thread pools.
Brian Goetz's point about reinventing the wheel is also well made.
Also from developerWorks recently - Introduction to the Thin Client Framework.
Ned Batchelder on Erroneously Empty Code Paths. Wise words.