Personalized letters are significantly simpler if you know how to use a spreadsheet to fill in the blanks (and write your letter so none of the blanks need to be adjusted post-merge). However, there is no special technology to prevent you from, say, using a form letter and hand updating data that wasn't on your spreadsheet and missing a merge field in the concluding paragraph so it reads,
Yup. Definitely feels personal now.
Ugh. Technology, I love and hate you.
**Update, 1 minute later** Definitely posted this to a group blog I'm a co-author on that was somehow on the top of my dashboard instead of to my personal blog. USC Honors College Class Captains, I apologize. Apparently, today's mistakes are not limited to merge errors.