Pitchfork has an interesting feature where indie outfit Galaxie 500 breaks down the money they recieve from popular streaming services Spotify and Pandora. The short answer? Not much. The longer answer is a little more interesting though:
Galaxie 500's 'Tugboat' was played 7,800 times on Pandora in the first quarter of 2012, for which its three songwriters were paid a collective total of 21 cents, or seven cents each. To put this into perspective: Since we own our own recordings, by my calculation it would take songwriting royalties for roughly 312,000 plays on Pandora to earn us the profit of one-- one-- LP sale. (On Spotify, one LP is equivalent to 47,680 plays.)
One thing the Pitchfork article omits however is that both Spotify and Pandora are losing money - and not insignificant amounts. Spotify lost $59 million in 2011 and Pandora lost about $0.20 a share in the previous quarter.