Thank you for the responses so far. So (on balance) I'm not going mad or becoming a boring old fart.

I don't expect people to be utterly attentive all the time they're not actually playing or singing - sometimes there are quiet conversations (often music-related) going on during a tune, for example. But at least that is still engaging and bonding with the people who are present in the room, rather than with people and events elsewhere.

Those who defend the habit might like to consider the "What-if-everyone-did-it?" argument. Imagine a session or a club where all those who were not actually playing or singing at any given moment chose to start reading Facebook, checking the football score or texting their friends. We'd lose the whole social cohesion and "crack", and the sense of shared experience that we (presumably) came there to enjoy.

Controlling it, though, is tricky. If it's a club, the MC could try to lay down some rules, but in an open session in a bar there's not much you can do - or is there? I do run a pub session, and am considering, next time I send an e-mail to remind people of the date, suggesting that they refrain from unnecesssary noodling on gadgets. Would that be acceptable to most of you who attend such sessions?

Marje