Any time an inductor is put into a power line, the purpose is to present a series high impedence to AC current. They work in series, similar to the way capacitors work in parallel (shunt) to provide a low-impedence path for unwanted AC currents. In the case of a microprocessor, if heavy pulsed currents are being pulled off the Vcc line, the inductor may be used to offer some isolation from induced ripple to the more critical reference line (AREF).
(edited spelling 1-3-07 R.L.)