Friends Reunited?

Every so I often I like to have a look round friends reunited. We've all done it, how many times have we found someone we went to school with and thought *******, they were the thickest in the class, and now they live in Norway with their own fabulous business and handsome/beautiful Norwegian spouse.......?! Or something like that anyway! So I was looking this week and came across someone who was ostensibly a best friend during my teenage years, and our parents are still very good friends as well. So whet do I do? Do I drop her a line and say nothing, do I say hello and spill everything, do I try the tactful approach, or maybe just letting sleeping old friends lie is best? After maybe that's better than having your mail ignored. Hmmmmmmm..........