I went to Disneyland grad night back in May.
Things to Know:
Fastpasses aren't in use.
Toontown is closed.
You have to walk to the gate from the parking lot, trams aren't in use.
You aren't allowed into the park until 11:30 PM.
When I went, the only rides that had a major line were space mountain and indiana jones, 1 hour each. Everything else was about 15 min. Make sure you book it over to space mountain first. Here's the list of rides I went on: space mountain, pirates, splash mountain, thunder mountain, matterhorn, autopia, indiana jones, haunted mansion, Mr toads wild ride, teacups, and astro blasters.
Overall, I had an awesome time. I thought the park was going to be swamped, but it was the exact opposite. Have a good time!