Write it down
Journaling the details of interesting conversations you find yourself a part of can pay huge dividends in the future. Not only will you accumulate a wealth of valuable knowledge and ideas but you get the added benefit of seeing patterns emerge as you collect more and more data.
Also, by writing things down you force the amorphous cloud of abstract thoughts floating around in your head into something coherent and useful. This process is difficult, but important if you want to move your theoretical ideas into the realm of practicality.
This practice can be especially useful in a business setting where the entire group involved with the conversation will benefit from your efforts. Sending a quick follow-up email after each meaningful conversation shows that you care and can help keep everyone on the same page.