I commute 84 miles per day. If I were actually getting the 19MPG rating that the EPA gave my VW GTi, I'd be using up almost 4.5 gallons per day. At current prices ($2.13/gal as of this afternoon, for me), that's nearly $10 per day. Multiply that by 5 days of work for 4 weeks and I'd be paying out $200 per month getting back and forth to work. As it stands now, though, I'm roughly averaging 27MPG. That's 3.1 gallans per day, or $6.60 per day. In 4 weeks, that's $132 per month. I'm saving about $68/month by hypermiling.
The fact that I don't forgo things like windows down and sunroof open on beautiful days while still travelling at 60+MPH or that I still actually do 60+MPH speeds, I think that getting almost 45% above my cars EPA FE rating is amazing. I find it to be rather fulfilling to push this envelope.