Earlier this month, Steve Henderson from the DMA (UK) shared best practice guidance on how to use registration forms to get permission to send follow up email marketing. It's solid guidance and those looking to better understand how to list build using registration forms should check it out.
Spamfighters might get a bit itchy about some of the language used (whether or not some of this constitutes opt-in or opt-out) but the fact of the matter is that these processes tell people up front that they're going to get email and allow them to choose to get that email or not. That's what I would call permission, and if everybody did things this way, spam problems overall would be greatly minimized.
This is solid Email Marketing 101 guidance.
[ H/T: All Things Email ]