Why does the Uno have two microcontrollers?

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?

The ATMEGA8U2-MU does the USB to serial bit and replaces the previous dedicated USB chip. The other is the arduino processor that you program.

Thank you Grumpy. Thank you very much for satisfying my curiosity.