There was a good analysis of it on the Today show. It's mostly partisan politics. Hillary jumped all over Bush for it and the Republicans have said she should shutup as she turned a blind eye to what went on when Bill was in the White House. Bush's polling numbers are so low that the only people he has to keep happy are his core constiuents, so he commuted the sentence to keep them happy.

>Bush has commuted Scooter Libbey's sentence.
>
>Bush said "I respect the jury's verdict. But I have concluded that the
>prison sentence given to Mr. Libby is excessive. Therefore, I am
>commuting the portion of Mr. Libby's sentence that required him to
>spend thirty months in prison."
>
>Huh? You respect the verdict, yet commute it??
>
>and he also said
>
>"My decision to commute his prison sentence leaves in place a harsh
>punishment for Mr. Libby"
>
>a $250K fine is pocket change to these people.
>
>
>This is a complete betrayal of the American people . . . But then that is
>nothing new to Bush.
>
>This is the guy who was going to bring integrity back to the White House and
>also the guy who said "if anyone in my admin was involved the Valerie Plame
>leak they will be fired." Can you say hypocrit?
>
>And the republicans impeached Clinton. Go figure.