Film Score Monthly has an interview with composer Nicholas Hooper (who did the soundtrack for Order of the Phoenix and Half-Blood Prince.  In it he states that he will not return to score Deathly Hallows.  He also says he hopes that John Williams will return to finish out the series.

I actually decided I wouldn’t [return]. It impinged on my life and my family too much to do it again. We managed to cope with two of them, and I just felt it was time to hand it on…”

Read the whole interview in the latest issue! Thanks Leaky.