I think other than some balance issues, most Corps used them relatively effectively. They weren't used as a mainstay of anyone's show, and I think that this year actually had a lot LESS percussion-only breaks than 2008. It seemed to me that there was a whole lot more full ensemble playing this year, instead of just park n bark, then run around while the pit plays.
Then again, I haven't watched the DVDs of 2009 repeatedly like I did with 2008, so I could be wrong.