As a Magento partner, we have just received the following briefing regarding Paypal adoption and usage:
• 143 million active registered accounts in 193 countries
• Increases sales and improves conversion
• Supports payments in 26 currencies around the world
• Net total payment volume was $180B in 2013
• Processed $27B in mobile payment volume in 2013 up almost 100% from 2012
Seems a no-brainer to add it to your Magento store as - mostly - it only takes a few hours to install and test.