I initially enrolled in their 10% wind energy program as they were offering rates guaranteed to be lower than BGE. I'm currently on their 100% wind power program. I think it increased my bill by only about 10%.

I switched to Pepco Green in 2007. (Don't confuse Pepco Energy Services with Pepco that delivers electricity). There are periods when the rates are higher than BGE, but I personally think the other 'costs' of non renewable sources and the pollution they produce are greater considerations than just price.

Here's the description of Green energy from Pepco Green site:
Green Electricity is generated from renewable resources, which includes hydroelectric plants, solar panels, wind farms and biomass fuels. The generation of Green Electricity produces almost none of the pollutants commonly referred to as "greenhouse gases". These pollutants (such as carbon dioxide, nitrogen oxide and sulfur dioxide) contribute to global warming, smog and acid rain, and can result in damage to the environment.

It's more of a life choice decision than an economic one.