You are right Ian,
People are far more likely to open one from someone they know than a stranger. Your subject line has to be pretty amazing for a "cold" e mail to get opened.
I had a virus decimate my computer recently (even with so called anti virus software present). I opened an e mail that I thought had come from a customer. Now, unless I know the person / company, I routinely delete anything that I do not recognise.
I think we are also approaching the time when regulations for unsolicited e mails get tighter. It may be that sometime soon, we may only be able to send them to opt-ins. Won't stop the spammers though.