To those that care; I asked/contacted Spotify. They responded and said AAC 256kbit/s.
So not top notch but better than Slacker.
Can you swap back and forth between the 2 and see you notice any different?
That's really good compared to the alleged slacker rate of 64Kbit/s. That's what I recall seeing in an old thread on Slacker bitrate.
My Slacker account is giving me 320 bits.
If I remember correctly Slacker streams to our TM3 at 192. So it's an improvement. Looking forward to hearing it. No V10 for me yet.