Yes, indeed, and my project uses AVRs (and the Arduino environment) for the microcontroller as well. Sorry, I thought that would be obvious, as the MCP23008 is a "dumb" I2C port expander. :) So, to be correct, I should have stated that my project uses an Arduino to control an MCP23008 which runs the LCD. The advantage of doing this is that it only requires you to wire the MCP to the I2C bus on your project, instead of consuming lots of I/O pins.
Since the Nokia screen has an SPI interface (unless I'm confusing it with another common screen) it was probably not the best example for me to mention. But basically, I'm looking for information on people using a MCP23xxx port expander with an Arduino to drive a "larger than the typical HD44780" LCD.