The ones where you post your most listened artists in a certain week.

I recently signed up to LastFM (igakarate) and I'm not sure I get it. I know essentially these threads are just an excuse to show off about what you are currently listening to and I get why people would want to that but... how does it work? I mainly listened to music using my iPod or I listen to the CD's at home through my stereo. I have LastFM connected to my iTunes. When I plug in my iPod will LastFM be able to see what I have been listening to? Or is this for people who mainly listen to music through their computer?