Back in 2004, I did Disneyland and Knotts Berry Farm over labor day weekend.  On the Saturday before labor day, I went to Disneyland from 4pm to midnight.  I just got into the LA area an hour beforehand (thats why the late start).  The park wasn't very crowded at all. Not a long wait for anything. Fantasy Land was empty after 9pm, so I did all the kiddie rides.  
  
On the Sunday before labor day, I did KBF.  In the morning it wasn't too bad, but it started to get crowded in the afternoon.  Left at 6pm. 
  
On labor day, I did Disneyland/California Adventure (started off at DL, then CA, then back to DL)  It also wasn't crowded at all.