Other reviews have mentioned the problem of sites requiring a different syntax for passwords than PwdHash generates, and there are a number of different possible problems here. For some, the generated password is too short or too long, others require special characters in the password that PwdHash doesn't generate (others forbid these characters).
But I've encountered a couple of other problems as well. For some sites, it just doesn't generate a password, but leaves the master password you type, which gets sent to the site. I now know to type in the confirmation password using the opposite prefix (@@ vs F2) than I used for the original password. If the site says that they don't match, I know that PwdHash didn't work. Often, I can look to see if the number of asterisks changes when I tab out of a password field; if it doesn't, then PwdHash didn't work, and I don't have to submit the form to find that out.
Another problem I found is on some sites, I was able to successfully create a password,
but when I went to log in again, PwdHash told me incorrectly that the caps-lock was on after I typed the F2 key and a single character. If I typed @@ and the character, it told me that my password was too short to protect.
Queries I made about these problems to the authors have been unanswered.