A standard Prius doesn't plug in anywhere, so there is no associated coal power plant pollution. I recently saw a bar chart showing the total emissions for each type of fuel, taking into account the emissions from the plant generating the electricity, and IIRC the hybrid did better than the plug-in all electric. Sadly, I can't find the chart right now.
I will agree that, it generally only makes financial sense to have a hybrid if : a) you put substantial mileage on your car and b) gasoline prices are high. In my case, I have a 2008 Honda Civic Hybrid. I drive over 100 miles per day and gas prices here in CT are very high. When I bought the car, the federal income tax credit and state sales tax elimination made the cost of my hybrid equal to the cost of a regular Civic, so the savings were immediate and substantial - roughly $800-1000 per year on gas. However, given that I recently had to pay $2400 to replace the IMA battery pack, I'm probably only about $3500-4000 ahead after 7 years.