Hey, I’ll weigh in on this . . if you are getting good clean traffic, single optin is usually good. You’ll know if you need to switch to double because you are getting too many spam complaints – but honestly, if you are getting too many spam complaints generally speaking either your emails are not good and people don’t like them, or you are getting lousy leads and that needs to change.
Autoresponder companies like double optin because it tells them someone really wants to be on your list.
I believe that I should focus on ONLY getting folks on my list who WANT to be there, so I’m ok with single optin, because of my targeting.