I have answered my own question - "sometimes - normally as something of a brief encounter".    I love meeting people and learning a little about them, their view of the world, and why they are travelling. 

When cruising (and that is not alone - it's with Lisa) we often join other tables with random other cruisers for dinner - random in that they just happen to be the 3 or 4 other couples, or singles, who have turned up at the restaurant "happy to share" at the same time. But very, very rarely do we hook up with / latch on to others - the world is full of so many different people with different interests and just as I am a travel / transport / dog bore to them, so we I enjoy hearing about their  DIY / golf / fishing / housekeeping / grandkids exploits in small doses, and their politics out of interest to understand and not because I share their views.

When on a train,  I / we sometimes have encounters and strike up conversations.  Far more so on the more countrysideesque lines that in the urban areas and cities.  Fascinating and I can enjoy a journey chatting (in fact I often wish the ice had been broken earlier in the journey to learn more), but very rarely indeed is there anything to be ongoing beyond the journey, or would I want to be accompanied by that same person on a significant proportion o my journeys, or for more than a day or two.

That reminds me of an anecdote from one of my fellow van drivers, years ago.  Apparently her brother, a motorcyclist, was enjoying a casual bike ride in Windsor Great Park when he saw two equestriennes (females on horseback, for the benefit of those not familiar with the term). He pulled over, stopped the engine and sat down to make a roll-up cigarette while they passed.

They actually stopped and started to chat with him. After a while, it apparently began to dawn on him that he recognised them from somewhere. They were indeed the Princesses Beatrice and Eugenie, out for an informal ride in the park. 

Met with better fortunes than did teenage us when, seeing one of the only useable lengths of Thames towpath, we hopped ashore to tow the boat. Unfortunately, that stretch of around 1 1/2 miles of immaculately maintained path is part of the private chunk of Windsor Great Park and we only managed around 100 yards of towing before various security guards arrived to chuck us off.

How that length of the navigation worked when the path was needed in anger I don't know. 

Perhaps, like much of the rest of the Thames navigation, it didn't work particularly well, one of the reasons why canal companies were desparate to bypass it entirely - their ambitions for the most part thwarted by the influences of the Thames Commissioners.

Mark

While I don't seek out meeting people on days out, some chance encounters that I've had can be most rewarding/interesting/entertaining.
Only a few days ago during a trip to Cardiff I had occasion to strike up a conversation over a drink (ot two) with a charming American lady on a "networking" business related trip....to London....but took a train, on a whim, to Cardiff for the day before flying home because she'd never been to Wales.
What followed was a very interesting chat with her for an hour before she had to go for her train.  Totally unexpected and a pleasure.

We're going off (again) at a bit of a tangent here, but I do remember BBC^» (British Broadcasting Corporation - home page) news reporting from the day after the wedding. They had footage of Mr Middleton, sitting on a motor mower, cutting the grass in their garden.

Well, if you've just had the honour of giving your daughter in marriage to the heir to the throne, life will go on - and the grass won't cut itself.