Spotify invite last night when I was waiting in line to see the midnight showing of "Harry Potter And The Death Hallows Part 2." I had my Spotify account up and running and I was listening to music before I got into the theater.
You can go ahead and download the Spotify iOS app [iTunes link] and request an invite on the website.
So far, I like what I hear.
I chose the high quality stream (320 kbps) and I think it sounds better than Pandora and doesn't stutter as much as Last.fm.
I bought into the $9.99/month deal that supports mobile streaming and offline playing. Otherwise, it's desktop-only. If you're going to stream music from mainly one desktop computer, it's a FREE service with ads. If you really, really abhor ads, you can part with $4.99/month plus the ability to login from any computer without restrictions.
In iTunes, social interaction through Ping seems like an afterthought. I don't use it everyday. In the Spotify desktop app, you login to Facebook and immediately you see friends who already have Spotify and public playlists are easily shared. Right now, I'm enjoying listening to my friends' playlists more than my own. If you have Spotify go ahead and add me:
Rdio and it was a decent service. But, I never figured out how to enable offline playing so I couldn't play songs in my old car. And I don't remember sharing playlists. The main difference is there is no free version of Rdio and the desktop player is within a browser.
I will try this service at least until iCloud is fully implemented with iTunes Match sometime this fall. Although iTunes Match only streams the music you already have in iTunes, it's also much cheaper at $24.99/year. iTunes Match streams up to 256 kbps, which may be good for some who don't have unlimited data plans. Is Spotify worth $119.88/year for me? We'll see...