I just did a blog post about using Dropbox from Ruby since a Ruby-based library had just been released. Adding a note saying "If you're not yet on Dropbox, sign up here" and within a month I maxed out my account. Indeed, I switched the link around a few people who asked if they could do it too.

Given how much traffic you can get with a simple but smart blog post nowadays (especially with HN and Reddit around), use content marketing instead. It's easier, gets you more kudos, and only costs a little time.