Tip for bloggers that use pop-up forms
Sometimes people don't feel like filling out yet, another optin form.
I've tried this on a two of my niche blogs and it's made a big difference. I don't know the percentages as of right now. But, just from eye-balling my stats, I've noticed a significant increase in subscribers.
What I've also noticed is that a lot of my RSS subscribers eventually fill out my forms and subscribe to my newsletters anyway.
I hope that you find this info to be useful