Really, I see the song buy back program as the only real way MS will be able to catch or overtake Apple in this arena. If they are going to compete they almost have to do this.
Personally, I have invested quite a bit of money in song downloads from Apple. No way I'm going to surrender these. Moreover, MS has to hurry to get in the market as once movie start to be available for download the game will be over. Hard to imagine anyone buying back movie downloads.
If Microsoft does do the song buy back program, I'll buy their player just so I can hedge my bets. I've got nearly $2,500 in iTunes music and it would be worth the $300 (to buy the Microsoft device) in order to get all my music in WMA format as well.