According to ESPN the deal is done.
Probably a good move by Utah as Deron wasn't happy there - and he wasn't doing a great job of leading the team this year, as shown by his negative +/- for the season. (While the +/- is not a great individual stat in general, its the perfect 'bottom line' stat for PGs. For the starting PG of a team playing better than .500 ball to have a negative +/- is pretty damning. Devin Harris has a negative +/- too, but everyone on the Nets is negative and Harris is somewhat better than the team average.)
I won't be a bit surprised if Utah starts playing better and winning more with DWill gone. Not that I expect Devin Harris to be all that wonderful for them but he won't hurt them and the whole team will pull together.
If Favors lives up to his potential and they make something of their draft picks Utah could come out ahead on this deal - well ahead if you figure they'd have lost Williams next year if they didn't act. Of course, the new CBA may throw a monkeywrench into it in some unforeseen way.