Fast Company took a look at two different marketing uses for Twitter – promoting a new Soulja Boy album and a Toyota promotion for new owners – to determine the value of a Twitter campaign.

In the case of Soulja Boy’s new album, despite a barrage of tweets to his 2.5 million followers, only 13,000 copies of the new album, “The DeAndre Way,” were sold in the first week. Compared to the 45,000 copies of his previous album sold in the first week, this one was a bust.

New Toyota owners were asked to tweet a specific message for a $500 reward that they can claim by January 3, 2011. The Fast Company story doesn’t mention how many of these tweets they’ve gotten so far or what the goal is. However, “essentially Toyota’s PR team are valuing each of these tweets at $500 worth of promotional material,” the story reads.

Concluding that Twitter is “a tool that you have to use intelligently and carefully in order to convert digital action into hard sales,” Fast Company looks at these campaigns from a cash perspective. But that may be just one metric for success (albeit an important one).

Increasing awareness and loyalty for future campaigns, programs, and offerings, which is harder to measure, might also be a byproduct of these campaigns. Soulja Boy, the story says, is popular for singles rather than full albums. Toyota is in the middle of rebuilding its reputation. For both of them, building and maintaining reputation through this and other social media campaigns could be priceless.