OK i am willing to take the first shot at this!
"Extent of your involvement in other's life:
siblings - I feel that there should be consistent interaction with siblings. You warn them when they are playing with fire, and support them whole heartedly when they are successful. Of course interfering with personal life (life-partner, etc.) is not justifiable except of course it is to support the right thing and IF asked for input. I would support the truth regardless of who is saying it - my bro/sis or their other respective other halfs.
friends - Similar to siblings, but interaction should be limited to warnings or truth...should never lead to undue arguments. With siblings, arguments are OK because ultimately your love for them is not questionable. With friends there is a limit to interference. Also, you dont want to be responsible for any breakups because you lose friends forever because of things like that - plus the burden of guilt would be too hard to bear.
collegues - No personal interaction at all...except to learn or inform about personal achievements or updates on family matters. I prefer to keep my colleagues as far away as possible from my personal life...i would inform them if i was going to get married or have a kid or had a death in my family or a divorce, or some such life-changing event...but i would not go into any details with co-workers.
own kids - Constant interference until they are old enough (18-21) to be on their own. After that the relationship changes to that with siblings... no interference with their choices unless they can really harm them without their realizing it. My experience with my parents is pretty ideal in this respect. Until i was a kid, they interfered with almost everything, and i did not make very many major mistakes. After i have become an adult, they point out errors in judgement - and are not afraid to get into an argument with me...but their intentions are never questionable and i often end up making an informed decision, regardless of whether my decision is to their liking or not. It is a question of knowing the risks thoroughly rather than accepting their "bottom line."
neighbours - No personal interaction at all, unless asked. Similar to colleagues in a way. But i would be more willing to respond to their queries rather than volunteer any suggestions on my side. I would definitely not like to involve them in any of my personal issues at any cost. Because if something goes wrong in your own family, at some point you can forgive and forget the perpetrator. Your neighbors may not be that willing to forgive or forget and can cause future problems.
where & when to draw the line" - everywhere and often 
Siblings - Not at all an expert at this...
Friends - It is really difficult to decide where to draw the line. Sometimes we tend to feel that the friend is not doing right, but not sure if the friend will receive our criticism on it. But again what is the use of friendship if we cannot pull the ship ashore without sinking. It is very rare that one has true friendship without any kind of expectations.
Colleagues - I do not like to have a very good friendship with them.. I prefer being professional. It is so often that we give peer reviews and it is going to be very difficult to give an unbiased review. Have been bitten by giving a review and lost a friend. 
Kids: I would like to be as involved as possible with them - socially, hobbies, studies you name it. Girlfriends, boy friends.. the list goes on. I think byt the time they are in their teens they need to start tasting independence with a rope though... and then of course hope to be like my parents and in-laws who keep telling me that they are the peripherals in my life and not the center point.
Neighbours - Hello, How are you... let me know if you need anything.. can I hold the mail for you.. I have not had very communicative neighbours here.. so do not have anything much to offer.. but I think unless neighbours are friends, we cannot really have a relationship.
Parents - Make sure they still are a part of my life, that they are not ignored.
simply bcoz they are easily accessible and the same thing from their side too. Now, I cant even think of having same kind of relationship with my desi neighbours here. They are simply acquaintances, even though we meet often for potlucks or some kids activities.
I tell him so. If he agrees, good, if he does not, then I back off
