I read Seth Godin's blog today. He was asked how to build an e-mail list. He answered:

"I told her that the first step was to offer something in your email newsletter that people would actually want to read. That the second step was to promise people exactly what you intended to give them. And the third step was to create content that was so remarkable that people wanted to share it. I explained that if you take your time and keep your promises, it'll build if it deserves to build."

Pretty interesting..