If I can get Keyboard + Arduino working, my plan is to send data directly into a waiting Excel workbook.
Follower (Philip Lindsay) has done that. He's put details on his site:
http://code.rancidbacon.com/ProjectLogArduinoUSB
I've since done the same thing and documented it for Practical Arduino (coming soon). Relevant links include:
Arduino pretending to be a keyboard:
Arduino pretending to be a keyboard to control a game using a Nintendo DS touch screen: