I just wanted to point out that while I think this is really cool and interesting work, there is a much simpler way of getting the data into a Google spreadsheet using IFTTT that I wrote about here:
Both ways are good and I know you mention the simpler way in your readme. I would say that your method is certainly more advanced but beginners might have an easier time with IFTTT. Also by using IFTTT you can at least separate out the event name, timestamp, device, and event data into separate spreadsheet columns, so some of the pains associated with other methods are not there.
Here is some test data from last summer that I have saved--there are a lot of computers in my home office so it really was 90+ degF.
The columns are Event Name, Event Data, Device Name, and Timestamp. The spreadsheet has formatted the timestamp into a more human readable format, but you can turn that off.
Thanks for sharing this, especially your firmware!