I recall some time ago that this feature was briefly discussed and to be implemented eventually (after iOS), and just wanted to add further suggestions.
The basic idea is that different lists should be able to have different levels of aggression or priority in the adding process. My lists associated with formal studies (following a textbook at a fixed pace) should take precedent over those lists that are just miscellaneous words I've added via the Zhongwen plugin or other random sources.
Additionally, I'd like if I could specify the maximum number of words that can be added per day per list. My textbook lists would have no limit, as when I add a chapter I want to study the whole thing (through the natural adding algorithm), but my Zhongwen list would be something like 5-10 words per day. That's because the Zhongwen list can grow very quickly and I don't want it adding too many words and swamping out the textbook related reviews.
Finally, it would be nice if words to be added could be prioritized by their frequency. I already have my own process (before adding to Skritter) for sorting miscellaneous words from articles and readings using http://mandarinspot.com/annotate and then only adding the 10 most frequent words, but it would be nice if Skritter could do this automatically (perhaps during the adding process - paste in a set of 50 words and Skritter knows to add only the X most frequent of them if a box is ticked).