Why Does My RSS Subscriber Count Vary Daily

I use Feedburner like many bloggers to manage my RSS feed, and have always wondered why my subscriber count varies every day.

Apparently it's primarily because of people using stand alone feedreaders (as opposed to Web based ones like Bloglines and MyYahoo!). If they don't turn on their computer and start their feedreader, they don't get reported that day.

Full details at Problogger, as Darren took the initiative to research and answer this common question.