I launched http://marrily.com early December 2011, and within a few days I had the first sign up. I didn't advertise at all but had a soft-launch on HackerNews. Since then Marrily got mentioned on a few magazines (Brides, and NYMag) and totally via organic sources (they found me and reached out). I did a bunch of give-aways and sponsored-posts too. Building partnership is important since it creates endorsements and synergies. Depends on the industry, but for wedding in particular, traditional prints still give very good results. Even 6 months after the printed article on NYMag, I still have vendors contacting me for partnerships and new customers signing up via that source.

My current pending failure is that I haven't made much progress since the launch but ended up getting a full time job for a while to rebuild my savings. I spent all my money working/not-working on Marrily and I was pretty broke when I started working again. I'm not giving up, but more or less spend some time to grow personally and professionally so when I resume, it will be another exciting stage of the journey.

BTW, Rob Walling's interview in babuskov's comment is really good, full of food for thoughts.