Yup. If you run opt-out rather than confirmed opt-in mailing lists, you will get blacklisted by spamhaus and the like, and kicked off of many ISPs. Opt-out, rightly or wrongly, is generally considered to be spam.

Now, I'm not saying opt-out can't be effective; I'm sure it is, else people wouldn't do it. But it does show a certain lack of respect for my time.