This is in India. They sent me the NDA copy which states 5 years expiration :) Isn't this something to be done before joining the company and not post quitting? I told them that I have no intention of competing with them nor stealing their ideas/customers. But they are very insistent and almost pestering me now.

I certainly would not, as you would be more restricted in your freedom to communicate and opening yourself up to more possibilities of legal troubles down the road.

They would love it if you signed, but I can't see any benefit in it for you.

If they are pestering you, the NO, definitely not. Why would you sign something at this point? You already quit.

Cost/benefit? What's the cost, and what's the benefit?

From your description, it appears they are asking you to take on a "cost" with no corresponding benefit. Fail.

If/As you are under no legal obligation to do so, why do so? Is there some professional, relationship, or other benefit to doing so that you've not yet described here?

Always a culprit isn't it ? But IE10 so far looks pretty promising...

I would like to point out that the % of older browser usage is going down significantly. We are talking < 35% of web population and shrinking by the day ... http://gs.statcounter.com/#browser-ww-monthly-201111-201201