As far as I can tell, the only opacity shortcuts are:
10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%

That means the following opacities are missing:
0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%

Miserable!

We should be able to set any opacity with keystrokes. Tons of other apps have proven this concept. Adobe sucks.