ITunes Match will not match all songs

It's been confirmed elsewhere that metadata alone will not give success in matching (if it were, someone would quickly find a way to just create thousands of dummy files with the right metadata). Some audio fingerprinting is going on, and you can test it by changing the metadata of one track to that of another one, and see if if matches the audio or the metadata. Still, metadata plays a role as well.

MacWorld have a note on the problem of one or a few songs not matching from an album: Basically, it seem to affect specific songs (rather than just randomly failing every n:th song). Two possible reasons for this:

1. The audio or metadata specific to that track confuses the matching algorithm (as we know, audio fingerprinting is not an exact science)
2. There is a rights issue with particular tracks that Apple haven't been able to find agreement for.

If you enable iTunes Match, your entire library (up to 25.000) songs will be synced with your iCloud. So all your songs are in the iCloud. You can add a device to the iCloud and by so, all your music on the new device will be synced onto the new device. That's how iTunes Match works.

If you computer/hard drive gets stolen, you buy a new one and authorize it with you iCloud, it will sync once again on your new device.

So yes, you'll be able to download all your music stored in your iCloud onto new device.

As a matter of fact, even when the original device lost it's files, the songs are still stored in iCloud.

But be aware, the limit on devices is set on 10. So make sure you haven't add 10 devices already!

EDIT:
Proof of this is on the iTunes Match-page