Bit.ly has a great post up: You Just Shared a Link: How Long Will People Pay Attention?
In general, the half life of a bitly link is about 3 hours, unless you publish your links on youtube, where you can expect about 7 hours worth of attention. Many links last a lot less than 2 hours; other more sticky links last longer than 11 hours over all the referrers. This leads us to believe that the lifespan of your link is connected more to what content it points to than on where you post it: on the social web it’s all about what you share, not where you share it!
While the data is fascinating, the other big lesson here is to observe how Bit.ly got me to send a link their way. It’s not about where you share your linkbait, it’s about how you use your own data to create something really unique to share.