how to track social prospects & conversations

Does anyone know of a tool for tracking social media prospects and conversations? I am talking about tracking activity BEFORE a prospect would go into a CRM system as a lead, or do you just put them into Salesforce right away?

For example, let's say on Twitter that I start conversations with 20 physicians or retweet their tweets. I am thinking of making a spreadsheet of these 20 physicians and entering the data I know (anything I can get from their profile or geographic location), and noting that I talked with these people on Twitter on February 25.

Then let's say I reach out to all 20 physicians again one week later (on March 4). I would note that in the spreadsheet, along with any more information I learn about each of them.

And then let's say after 6 months of interactions I add them to our nurture email list, or introduce them online to one of our salespeople, or something like that -- and maybe then officially put them into Salesforce.

Does anyone have experience with this? Do you know of good software to use or any good articles?

Thanks very much!