I can't stand the self important fucks that put read-receipts on their e-mail. I only see it about once a week, but it drives me nuts whenever it pops up.
Only freaking idiots use that feature.
I never send the receipt back.
I also despise people who use the important flag. They immediately go down on my priority list.
Just send the email. If you aren't an abuser of email, I will respond in a timely (my time) manner.
If you are a salesperson and send me spam (any email that I did not request), then don't expect me to respond. And don't act surprised when you have to call to actually engage me.