Imagine designing a converter/charger with an integrated power FET for lithium-ion or lithium-polymer cells in Bluetooth headsets and accessories. Then, try making it work from either an ac adapter or USB cable without user intervention. Next, have it multitask by regulating the battery voltage when there's no external supply. And, squeeze it into a 3.5- by 4.5-mm QFN package.
Then again, you can try Texas Instruments' bq2501x family. Two versions have fixed 3.3- or 1.8-V outputs. The third version's output is adjustable between 0.7 and 4.2 V. Powered by an ac adapter, they'll deliver up to 500 mA. With USB, current is limited to 100 or 500 mA.
Pricing is $2.20 each in 1000-unit quantities.