Well, you'd need to implement some kind of webcrawler, which is parsing websites, since this is probably your target. Then you'd need to analyze their content, while it may be tricky to extract it from menus etc. Afterwards you'd need a way to store the data and somehow create connections to real people. All in all an interesting project, but very complex and probably hard to realize, since the results will be quite shitty.
Well, I guess that on computers it would be difficult to execute, but how about on phones? It's possible to create an app that monitors text messages and sends them to me, but could you use a keyword system to avoid tons of useless conversations? Could the system also monitor internet searches?