I write code, and subscribe to a lot of newsletters.
When I get an email that provides me with some immediate value, and then pitches me to exchange some money to deliver more value, I'm probably going to open up my wallet.
Peepcode is a great example. I'm not going to spend time checking back to see if there's new content, but I occasionally get emails for them advertising a new screencast. It benefits me ("Hey, I'm partially interested in X, and I can get a good baseline understanding of X for an hour of my time and $Y"), and I know for a fact I'm not the only "hacker" who gets these emails.
When I get an email that provides me with some immediate value, and then pitches me to exchange some money to deliver more value, I'm probably going to open up my wallet.
Peepcode is a great example. I'm not going to spend time checking back to see if there's new content, but I occasionally get emails for them advertising a new screencast. It benefits me ("Hey, I'm partially interested in X, and I can get a good baseline understanding of X for an hour of my time and $Y"), and I know for a fact I'm not the only "hacker" who gets these emails.