When people bring wine for dinner do you drink it or keep it? Our friends brought some beer and a bottle of red wine the other day as the wine was so cold we drank a bottle we already had, the beer was cold as well but obviously fine. It just occoured to me it may have been rude as I put their bottle in the rack.
Oh we keep it unless they say something like "we brought it as it will go so well with X" that we are having that night. Otherwise it's a gift and you can do what you like with it. Depends on the friends as well though!
I would say that either option is fine. If you already have a bottle in mind you should go ahead with it. What is rude is guests bring wine and expecting you to serve it (implying that your wine may not be as good).
However I do take note of the bottle, and when we do drink it I try to send a note about how we enjoyed it.
If you take wine to a dinner, you shouldn't necessarily expect the hosts to serve it, as they may already have chosen wine which they feel will go particularly well with the food. However they may decide to serve it - it's entirely up to them and either way is fine
If a guest brings a nicer wine than the one I already have in, I serve theirs (so as not to 'diddle' them!) If a guest brings a bottle of white wine that is colder than the one I have in (e.g. if I only bought it an hour earlier and it's not thoroughly chilled yet, whereas theirs is right out from the fridge) then, again, I serve the colder bottle.
Generally though, I do find that when we have guests for dinner we drink the house dry eventually...