Certainly agree there on the "click" thing Fionas.

I think another part is also how well the husbands/partners and also kids click. I find it easier to maintain friendships when both families get along, so much harder when my DH thinks there DH is a 'DH" iykwim It helps to be able to organise family get togethers, especially with a lot of socialasion now restricted to evenings or weekends due to work.
This is my issue to Astrid. My friends partners, Andrew doesn't get along with. He isn't a very sociable person where as my friends partners are outgoing. Therefore we aren't invited to dinner or things like that (even though I am quite happy to go on my own) because of his lack of social skills.