Now available for those who would like access to all their music on the road.
I see this as a handy tool - even my 64GB iPad2 doesn't hold quite all the music I have in my iTunes catalog, and my 8GB nano isn't even close (though I realize it won't help that).

But a question:

It appears that I can basically replace everything I have purchased, ripped, or downloaded elsewhere with 256kbps versions on my PC - though not automatically.

So I'm curious as to how Apple will know that a track I have is valid. It says it won't match <96kpbs files, >200MB files, DRM files not authorized to that device But if I copy an existing file and rename it "Texas Flood.mp3" and put "Stevie Ray Vaughn" as the artist and "Texas Flood" as the album, how is Apple going to know that's not what it is?

Doing actual matching via the track contents would seem to be compute/network intensive. But if that's not done, I could basically make up 25,000 songs that I want via editing, match them, and download them. Is there metadata embedded within an mp3 file, encrypted/tamper-proof, that would prevent this?

One downside - when you replace files with 256kbps versions, they are AAC, even if the originals were mp3's.