As high as that? On other boards I have seen people having lots of problems over mailing lists. Non delivery, or delivery to an unvisited spam folder, of opt-in messages is a common issue, then of course people change their minds or just don't get around to it.
I guess I had nothing to compare it to, but if 50% is good, then I shouldn't complain. =)
I base it off what Feedburner shows as our actual email list (that you can download) versus active subscribers. The full list is about twice the size of our active list, so I figure we lose about 50% from the e-mail opt-in process.
In the past I tried resending the confirmations to batches of folks who never confirmed, but it never boosted subscriptions, so I figured either the messages were not getting through or the user had changed their mind. Needless to say I don't try to resend confirmations any more. It seems to be a waste of time.
There is definitely a lot of obstacles to consider with newsletters. We would not do it if we did not have such an automated process. Once you get past the opt-in blocks, you then also have to consider the reality of open-rates. From what I've read a 25% open rate is a pretty general average. Which means if you send out a newsletter to 1000 people, on average only 250 will actually open it. This is not because your newsletter sucks, it is just a law of averages. Folks don't always have time to read every email, or they are out of town, or they see it and just forget to open it and next think you know it is buried underneath other new mail.
So in reality you need quite a large list to be able to drive some serious traffic via a newsletter. We tend to get close to 2,000 "opens" of our newsletter that gets sent to 7,000... so we are close to average.
My goal is to grow our list over the next 5 years to the point where I no longer "need" search engines to help drive most of my traffic... that is the ultimate value of a newsletter in my opinion. Not necessarily monetizing it, but an investment in the future of your business.