Did you buy iTunes Match? Because otherwise your entire library isnt in the cloud.
Anyway.. iCloud isnt a streaming service per-se.. your library still gets copied to your device. If you have a purchase in the cloud that hasnt yet been downloaded/sync'd to your device, you can listen to it while it downloads (sorta like streaming) ..
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No, I haven't got iTunes match. I don't think it's available yet. I'm curious about how iCloud will change the iTunes experience once everyone
is allowed to upload their libraries to the cloud, specifically for those that store their libraries on external hard drives. I understand that with iCloud you can redownload purchased content, I just recall that Eddie Cue talked a lot about streaming in relation to iTunes match in the recent keynote.
I just went back and watched the iCloud part of the keynote again, and it seems to me like there will be a streaming component to iTunes match. I wonder how it will work.