I run a site with a daily e-mail list. Every day I get a few out of office replies from people who subscribe to the list.These are typically college employees, and their auto-response gives me their name, e-mail address, and job title. Since I know they already use my site and I now know who they are, I can target people to make link requests with a much more personal approach. It's probably unique to my specific niche, but it actually works really well.