Just an idea, imagine it could be a pain to implement:
Could Skritter send a daily "word of the day" email for each user? So it would select a word from "my words" and send you a little email with it, just for added exposure.
It could choose the word randomly, from what you've studied recently, forget a lot etc.
It's not going to make a huge difference, but you know, every little helps.
I'm guessing the biggest obstacle would be performance as it sends out a bazillion emails each day?