While this is a small sample size, the difference is immense. Last year, DRB% (or total percentage of defensive rebounds pulled down while on the floor) was only 11.4%, far too low for a PF. However, this year, after 8 games, while Udoh's offensive rebounding remains about the same, defensive is up to 18.2%. Per 36 minutes, he's gone from 3.5 DRB to 5.8 DRB. That's much, much better!
Others have pointed out that most bigs don't improve as rebounders over time but remain about the same. Of course, considering Udoh's length, that he started out injured and that he was not well trained last season, we may see an exception.