Social media can be a very effective mechanism for marketing as shown in this video case study produced by Shel Israel as part of FastCompany.tv. The campaign was put together by SeaWorld San Antonio and focused on a pre-launch campaign for a new ride at the park called Journey to Atlantis.
They put up a WordPress blog and uploaded raw content to Flickr and YouTube. They then worked the online communities focused on roller coasters to get the word out.
This is an excellent example of a simple, highly focused campaign and a well orchestrated effort to measure the results.