Is it proper to write on a business card when someone gives it to me?

Is it proper to write on a business card when someone gives it to me?

Phyllis Davis (Business Etiquette Consultant) gives expert video advice on: What are the most important and least important items on a business card?; When is it appropriate to ask someone for his or her business card?; How can I graciously ask someone for his or her business card? and more...

It's common to write on the back of someone's business card, though mostly at conferences. For example, you might write on the back that they are interested in your healthcare products, or that you should follow up and send information. But generally, it's best to wait until they're out of sight line to write on their business card. But at conferences, everybody's used to that. I just returned from a conference for 4 days, and I wrote on the back of many people's business cards while they were standing there to let them know that I was going to follow up and do what they asked.