Very frequently, I'll meet words that I just can't recall, even if I saw it moments ago. They're typically words referring to an abstract concept or a word I rarely use, such as 'negotiations', or words that have many synonyms, such as 'however'.
It would be great if I could see a list of the words I've had the most trouble with. That way, I could take that list away with me and concentrate on it.
These words are the main reason I ultimately abandon flashcard systems. I'd like more tools to overcome them.