It's pretty safe, although their insurance policies are smaller than that of licenses cabs (think $10k vs $100k). Drivers undergo background checks and are rated after every ride. Uber does not tolerate drivers who get less than 4 stars.

What makes it better than Craigslist is the convenience. Take out your smartphone, drop a pin on your location, and get a ride within minutes. Plus, you don't need to worry about payment, it all happens behind the scenes via your Uber account.