Pros:

• They are convenient
• They are durable and can be used more than once
• They take up less space in a landfill than paper bags (Washington Post)
• It takes 91% less energy to recycle a pound of plastic than it takes to recycle a pound of paper. (Recycling rates of either type of disposable bag are extremely low, with rates of 10-15% for paper and 1-3% for plastic.)
  

Cons:

• 500 billion to 1 trillion plastic bags are used every year, worldwide
• About 1 million plastic bags are used every minute.
• A single plastic bag can take 20 to 1,000 years to degrade
• The U.S. goes through 100 billion single-use plastic bags. This costs retailers about $4 billion a year
• Plastic bags remain toxic even after they break down
• Every square mile of ocean has about 46,000 pieces of plastic floating in it.
• The average family accumulates 60 plastic bags in only four trips to the grocery store
• Anywhere from .5% to 3% of all bags winds up recycled.
• Ten percent of the plastic produced every year worldwide winds up in the ocean. 70% of which finds its way to the ocean floor, where it will likely never degrade.
• 80% of Americans choose Plastic over Paper.
• 100 billion plastic bags are thrown away in America each year.
•  12 million barrels of oil are needed for 100 billion bags
• The oil used in America for plastic bags is greater than the entire oil demand of Iceland, or North Korea.
•  500 billion plastic bags are used worldwide.
• San Francisco had a cleanup effort, and figured out that in the end, it cost them 17 cents to clean up one plastic bag. Multiplied by 100 billion, you end up with 1.7 trillion dollars spent cleaning up plastic bags in the US.
• Only 1% of plastic bags are recycled
• Usually "recycling" a plastic bag means that the bags are shipped to a foreign country with lax to nonexistent "recycling policy," and just burnt instead.
• A bag-tax would greatly reduce use - Washington D.C. put a 5 cent fee on all disposable bags and saw an 80% reduction. Ireland did the same, but a 33 cent tax instead, and cut consumption 94% within a year.
• 4 billion plastic bags end up as liter annually – if we tied the plastic bags together it would circle the earth 63 times – that is approximately 1,792,000 miles!! (the circumference of the earth is approximately 28,000 miles around the equator!)