I received a low-pitched follow-up this morning. The invite (identity obfuscated to protect the questionably innocent) is below
Dopplr has a list of my planned travel, as well as the same lists of colleagues of mine. In all likelihood, if and when we are going to the same destination at the same time, we are going to the same event (and so associated group logistics (e.g. hotels, shuttle buses, tours, etc) might be offered)
Why wouldn't airlines want this business (to the point of discounting it based on number of travellers)?
Come to think of it, Dopplr should be asking me for my FFF (Frequent Flyer Federation). It's points & upgrades, far more than the chance of an invigorating identity chat back in economy (the part of coach at the very front where they serve you drinks/meals first but otherwise treat you with equal disdain to the group of high-school students going to a band competition at the very back) that will drive my group allegiance.