No really. It is useless and a lousy hack. It's just a way for Thomson and FhG to further milk the mp3 buzzword, one more time.
Useless format:
* The lossless part is stored in ID3v2 tags.
* Size of ID3v2 tags is limited to 256MB by specifications; as a result, lossless part of an mp3hd file can't be larger than 256MB.
Addendum:
Current tagging software isn't prepared to deal with this kind of situation, so you're going to see various disturbing behaviors such as:
* Very slow tag updates (near-full-file-rewrite with each edit).
* Heavy memory usage of tag editors.
* Retagging stripping correction data.
* Tag editing or even reading failures when approaching the 256MB limit because software will try to put each ID3v2 frame in a single memory block and allocating a single block of such size is likely to fail in 32-bit address space because of fragmentation issues.
From: http://www.hydrogenaudio.org/forums/index.php?showtopic=70548