As for me, I switched from the French competitor Deezer to Spotify in a heartbeat, when Spotify's client totally blew my expectations with zero latency.

So I guess it does help you win the game. But of course it's not the only factor.

I guess you're in the US, Canada or Brazil, because Rdio isn't available anywhere else. But Spotify is, and is doing well.

I choose Rdio over Spotify because it has a web client which probably means they couldn't leverage p2p even if they wanted to (without using a browser plugin).

That's interesting. One of the main reasons I use* Spotify is because it has a native client and not a web interface.

*I'm actually currently in a period when I listen to music which is likely to never show up at any professional music service, but when I feel the need for mainstream music again, Spotify will probably be my choice for several reasons including the above, despite their recent Facebook-login only policy (which doesn't affect me, but still bothers me a bit).

Is there any Flash involved? One of the biggest features in Flash 10 was the addition of p2p streaming.

Upgrading flash does ask me to close Spotify.

P2P in Chrome is around the corner: http://www.webrtc.org