I was there today (both DL and DCA.) The crowds seemed lighter than earlier in the summer. We arrived around 8:15 and walked on to Indy and Splash, waited in a 10 minute line for Matterhorn around 10am, etc. We left DL at 11am, but compared earlier in the summer when it was very crowded around that time, this was much lighter. We were at DCA a short amount of time, but at 1pm the lines were 45 minutes for Soarin' and Grizzly River Run, 20 minutes for the Sun Wheel, 15 minutes for CA Screamin'. Millionaire at 12 was only about 3/4 full, and the Animation building seemed much less crowded than earlier in the summer as well.
I know that many OC schools are not back in school yet (I go back Sept. 5) but it seemed like crowds are thinning out, and the heavy crowds of the summer are almost gone. Since this Friday is the beginning of Labor Day weekend, though, you might encounter heavy crowds.