We were there Thursday and Friday (9/12 & 9/13). We felt the crowds were amazingly light on Thursday. We spent most of the day at California adventure and then hopped to Disneyland after the world of color.
Friday was a different story. We ended up spending all day at Disneyland and it felt like it was packed. Ride wait times weren't terrible but the whole place was a lot more crowded. Fireworks were slammed. Of course, it was a Friday and the first night for Halloween fireworks and Fantasmic and MSEP were both happening.
We had a great time!
Friday nights are always packed for the parade and fireworks.
I'm pretty sure the Halloween fireworks started on Sept 6.
I wonder if I could pay for my next trip by bringing 1000 straws and selling them for 25 cents each.
See also what the article says about Starbucks eliminating them at 28000 of its stores around the world. 