Newsweek published an interesting tidbit from Andrew Romano about the environmental impact of toilet paper.
Some facts from the article:

• The average American uses 57 sheets of toilet paper a day
• Collectively, we burn through 36.5 billion rolls each year. 
• Tossing all the TP in America would save 15 million trees, 17.3 terawatts of electricity, and more than 473 billion gallons of water annually

In light of that, the author states that, "the environmental impact of bidets is minimal in comparison."