The Arduino Uno schematic (http://arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf) shows a chip (U1) labeled ATMEGA8U2-MU, and another (ZIC1) labeled ATMEGA8. I see these on the board: ATMEGA8U2-MU in the TQFP32 package and ATMEGA8 in the PDIP28 package.
Could someone please tell me why the Uno employs two microcontrollers? How are tasks divided between the two?