Nowadays, I almost only use Google Docs for my text processing needs. I needed to do a mail merge using data from a Google Docs Spreadsheet to a Google Docs Document.
After a lot of Googling, I found How do I mail merge from Google Spreadsheet to a Google Document?
I could not get the script to work by copying it into Google Docs. However, there was a link where I could invoke the script - and clicking merge documents will get you to a good result.