"70% of in-laws don't like each other. Rest 30% are good actors ;)"
Though there are many 'in-law' relationship, I will restrict to the most interesting and notorious relationship between mother-in-law and daughter-in law alone.

We all say that this is a male dominated world. It is true too. But there is one area where it is female dominated. Where else? It is in maintaining Family relationship. Family head is a male just for a sake. Men as they age, kind of stop dealing the family related issues (it is the most complex issue). [
If you are going to say "No, It is not the case in my family". I am simply going to reply "Yours is an exception". Even my family is an exception :)]
Lets move to the next family issue.
Right or wrong, we are having a social system where a girl who was living in a system for 20+ years is suddenly unplugged and plugged into another system with completely different setup after an event called marriage. Foreign agent in a system will always lead to chaos. [Multi Agent System students can elaborate more :)].
Got the picture?
A woman who has lot of powers vested with her gets an additional post called 'Mother- in-law'. Another woman with lot of confusions steps into a family to create more confusions. Though ppl utter this sentimental dialogue "you are like my daughter", they are called 'Daughter-in-law' to indirectly say "you are not my daughter"
"Karthik. You are a male chauvinist. Not all in laws have a strained relationship. I know in laws who live like mother-daughter" Please read the first line again. They are just good actors.
So having set the ground that in-laws will always have some problem between them, let us see what could be the reasons for that. There are many. Each one of use have a lot of stories in our own families. There are plenty of reasons to develop hatred. But I feel, everything boils down to 2 root causes.
1. Mother's possessiveness towards son. They just don't know how to react when another girl is asking for a share. Biological curse erases the fact from their memory that they are (/were) also a daughter in law to another women.There is another peculiar problem in a family with boy and girl. Usually Mothers show a lot of love towards her son than daughter. But this is only till both of them get married (
I am yet to experiment this in my home since all my sisters are married and my mother shows lot of love towards me till now.
Have to wait and see). Comparison done between the daughter-in-law and daughter is a major cause for problem again all because of the possessiveness problem.
2. For the girl, it is a complete change in lifestyle. The girl has to adapt right from wake up time to dinner time of that family.
Some eat lunch at 2PM, some at 12 noon. Some families don't eat breakfast at all and some family eat 4 times a day. Which chore to share with mother-in-law? How much tamarind to be added for Sambar? Am I allowed to wear night dress during day time too? My mother in law maintains a shabby kitchen. Hooooof. Complete mismatch
So what can be done to solve this problem? First of all, can it be solved at all? Is there any desired solution that is defined? Lot of questions before us.
For sure, we can't ask people to change. There is no point in asking too. But we can at least try to change the system and increase the actors percentage from 30 to say, 70.
The probability of in-laws fighting decreases as their proximity decreases. [Who is going to write a mathematical model for this? :P].

So whats the suggestion from my side?
"Karthik. Wait wait. I got it. Are you going to suggest atomic family? Don't you know the importance of nuclear family? Isn't it good for children to grow under the care of grand parents? Who will take care of the parents who have been taking care of us these many years?"
Come on. Atomic families need not be 10000 kms apart meeting once in a decade. They can be in the same city too. Why not, in adjacent streets too.
As soon as a boy gets married, he should be made to stay in a separate house with his wife. Let the couples visit both their houses during weekends, festivals etc. Let the children spend the entire vacation with their grand parents.
If one needs the help of other, say, a working daughter-in-law needs her mother-in-law's help to take care of children or an ailing mother-in-law needs the care of her daughter-in-law, both the families can live together during that time. Now won't there be a problem?. Simple. When people become dependent, they won't create problems.
Making the in-laws to stay at a 'handshaking distance' will avoid 'hair-holding fights' :)
I am pretty much open to your comments and especially suggestions. After all, your inputs may help me too :P