Back from our trip. We went to Universal on Friday 6/10. Got there just after opening time of 9:00am (although it was an early entry day for those ticket holders). The HP area was crowded, mostly people stopping and taking pictures. We went straight to Forbidden Journey, which had a 45 minute wait time posted. The wait ended up only being 25 minutes. We rode Flight of the Hippogriff afterwards, which was about a 25 minute wait. By the time we were passing FJ again, the posted wait time was 75 minutes, so it was starting to get busy (around 10:45).
We left to check out the rest of the park. Came back to WWOHP around 3:00pm. Ollivander's was a 20 minute wait (cool little show inside the shop), and we rode FJ again and only waited around 30 minutes. Went to all the spots where you can use the interactive wands; most only had a couple of people waiting (if any). We didn't go into any other shops besides Ollivander's, so I didn't notice if they were crowded. There were long lines for the butterbeer carts, so we didn't get a chance to try it.
Like a previous poster said, the crowds come in waves. Either hit it first thing in the morning, or wait 'til it clears out in the afternoon. Overall we really enjoyed it. The theming was really cool and the ride was just off the hook! Loved the whomping willow! All the effects were amazing.