I recently was able to book my ADRs and wanted (and thankfully got) Planet Hollywood for my last day. We love ending our vacation with some yummy drinks! There were only two times available for reservations all afternoon. I think it's so popular because Disney gives their guests a $15 gift certificate for the restaurant and people are just taking advantage of it?
There are a number of the chain restaurants that only release a small number of their reservations to the Disney system. I'd try calling the restaurant directly to see if there is anything. We booked T-Rex at 180 days and only had 3 time options: 5, 6 or 9 pm. We have to call to get any other time.
If you are prepared to wait a while you'll get in ok - we walked up last year and it was very busy but we got a table in about half an hour or so, just waited at the bar with a yummy cocktail.
I was just going to post the same. We just realised that we hadn't booked it!!!....it was available when we first started to look. But there doesn't seem to be any openings for dinner August 6th to 18th.