Roughly what’s your Opt-In Rate for Pinterest Traffic?

Hi, I'm experimenting with putting an opt-in popup on my pinterest sites (so far been monetizing with ads and direct article marketing) and was wondering roughly what sort of opt-in rates are you guys getting on your pinterest traffic. I find that more than 50% of websites on pinterest have an opt in, so I must be in the minority of people not building an e-mail list yet.