I'm pretty sure this cat is locked out over night. Fine in the summer, not so fine when it's -3'C.
In the summer this cat tries to get in to eat my cats food. This annoys me and probably my 2 cats, but if I was that bothered I would get a new cat flap. (We have a magnetic one, so do the neighbours, I think we need an infa-red one) 
So, recently this cat has been coming in to my house during the night. At first there was a bit off spraying going on (whether my cat or the neighbours cat I don't know) but now that has settled down, and last night my cat seemed to bring this cat upstairs to see us. 
My cat breaking out of the kitchen is one thing, but getting the other cat to follow him is another.
(The breaking out of the kitchen thing is a mystery in is't self. My only explanation is ghosts or a super cat- so lets not go there)
Any way, should I say something to my neighbour???? They have a dog they are not particularly good with, and 2 boys the same age as my DC they are very good with (my DC spend hours in there garden in the summer, and I can hear all is lovely) - but the parents are very quiet, and it's sooo hard to strike up a conversation. I would have to knock on their front door and I'm shy. 
Most people I've spoken to have told me the cat will be fine out in the cold.