Not married, but I run into exes often. We say hi, maybe a hug, a kiss on the cheek - but thats it from me. Sometimes they want to rekindle , but I'm not with them anymore for a reason, and breaking up with some of them was tough -- why light that fire again?
It gets interesting when you're with your bf or husband at the time you run into the ex, and he either knows or figures out that the other guy is an ex. You get a real good perspective on how strong your current relationship is. If, after you're alone, the bf starts asking "is he bigger than me", "how many times", "did he last longer", "did he taste better", "do you ever think about him when you're with me" --- I know the relationship needs work. If I decide its worth saving, I usually make up a white lie (if necessary) to answer his questions, especially the ones about size and do I think about him..
Bottom line -- I say NO to a romp for old times sake. The memories are all I want - and sometimes I want to forget him completely.