Mp3Pro is a new Mp3 standard, which basically comes down to the same sound quality with half the file size.
I don't believe it will ever be a success because :

1) software developers have to pay Fraunhoffer to put it in their product. (this also applies to Empeg if they want their players to play the format, the exact reason why I believe it's never going to happen)
2) it's not completely backwards compatible with MP3 - you'll need an additional plugin or it will sound horrible.
3) the only plus I know of -the smaller file sizes- is not that big a plus in the first place, especially since large HD's have become reasonably cheap.