Internet radio service Pandora has just announced a pretty significant milestone: 200 million registered users in the U.S. Pandora signed up its first user in 2005, and had hit 100 million users six years later in 2011. It only took them less than two years to add on the next 100 million.

67 million are considered “monthly active listeners.”

“We started this company to help people discover and enjoy music they love, and to help artists reach and grow their audiences. Only in our wildest dreams did we imagine what it would become. It is now clear that radio is changing, and that’s great news for music fans and for the tens of thousands of working artists who now have a home on the air,” said Founder TIm Westergren.

In celebration of the milestone, Pandora has released some interesting stats about the service:

• 200+ million songs streamed before 10 am every day, which totals out to about 8,000 songs streaming per second.
• 1.49 billion hours of music streaming in March (170,510 years worth).
• 400+ curated genre stations

Pandora last released some user stats back in January to celebrate the new year. In 2012, users streamed a total of 13 billion hours of music. If March, 2013’s numbers are to be repeated, we can expect Pandora to break this mark this year. They also saw a million+ songs froms over 100,000 artists and 1.6 billion total stations created in 2012.

Just a little over a month ago, Pandora was forced to do something “contrary to their mission” and put a 40-hour per month cap of free mobile listening – citing rising costs.

Here’s an infographic with some more figures from Pandora: