Removing words from practice and personalizing word decay
There should be a checkbox or bullet on the front page of the vocabulary to include/exclude from practice.
Once I choose to exclude a word from practice, I can never add it back. Or instead, it would be better to have a numeric setting for word difficulty. (ie, 1 equals faster decay, 2 equals normal decay, 3 equals never decay).
We know about the problem where you can't add a word back into the words we give you for practice and are working to fix that issue.
The decay of words is personalized in that we use information such as the number of times you've gotten a word correct/incorrect to figure out how quickly it should decay. We're working on making this model use even more individual information when estimating the strength of a word.