I bought Rumors for $8 and that gave me 20 GB of storage for a year. I'm in the process of uploading all songs from my iTunes to the cloud. And if I buy my music from Amazon the music is stored free and it doesn't eat up the storage you are paying for. And now Amazon has much of their music for 69 cents so I'm switching over for good.
This will free up 10 GB worth of music on my iPad. I'll just use the iPad's storage for iTunes movies and TV shows.
Now about the cloud player:
It only plays through the iPad browser (only tried Safari)
It will multitask so you can leave the player and go to another website or app.
When multitasking you can use the multitask controls including AirPlay. Controls on your IOS-friendly headphones work also.
From the get go this does everything necessary to play tunes from the cloud. I'm sure Amazon will make improvements to the interface so as of right now I am a convert.