Pop Up Opt-ins And Ranking ? Any Idea ??

[Hamza]

Hi,

I wanna put up something like pop up domination on some of my big niche sites that are getting decent traffic,

But I've heard that pop ups can hurt the rankings, is that true ??

Please speak from experience and not what you've heard.

Thanks a lot and have a great day
Hamza.

Edite : i don't mean exit pop ups, but opt-in forms that float in the page after a few secs from opening the page .