If someone makes an introduction on your behalf you owe it to them to tell them what came of it.
As I mentioned in my last post, making your requests to others relatively specific is actually more effective than making your requests entirely open-ended. Specific 'asks' get the other person's creative juices flowing and gives them confidence that you'll have a productive and positive conversation. Remember: An introduction on your behalf is an investment/expenditure on the part of the person making the intro.
With that in mind, I think you owe it to the person who went out on a limb for you to tell them what came of the introduction. Did you meet and have a great chat? Are you going to work together? Did you learn something amazing?
There are at least three good reasons to do this.
One, it's just good manners to say thank you when someone has done something for you.
Two, that person who did work on your behalf may have concrete interest in the outcome of the conversation they spark.
Three, to the extent that 'knowledge is power' you can "compensate" the person who made the introduction by giving them an slightly fuller picture of the world.