Keen eyed players of Borderlands might have noticed that the Steam version recently updated itself, bringing Steam Cloud save synchronisation and something called BTest. According to the update, BTest is a stat tracking system that will record what guns and areas are most popular with players, in order to help Gearbox improve their games. The software also includes a leaderboard at Gearbox Labs , which will let you compare your stats to other players.
With Borderlands 2 announced for April next year, it seems likely the data collected will have some influence on the development of the sequel.