The Chicago based 3 year old popular music streaming service, Pandora.com, has just announced, via Twitter, that they have just reached 20 million registered users (8 million of these accounts have been active in the last 90 days). The company has gotten just over $20 million in VC funding in total. According to Compete, Pandora visits are up 51% year over year, with Pandora getting about 500,000 more visitors every month compared to Last.fm. Pandora still has licensing problems and is not able to provide its service to people outside of the US.