I find that using Skritter becomes increasingly difficult as the number of characters and words grows, and you have to work harder and harder to keep up. One way to relieve this a bit could be to add the option of creating a weekly schedule, where you could add words only on given days, giving you the other days for repetition only. For example, perhaps you don’t want to add words during weekends, add 20 words on Mondays and 5 words each day from Tuesday to Thursday. What do you think?
There’s a goal mode in the works which should make this a lot easier. However, in your example of having set days where words are added, and set days where words are only reviewed, this actually is the same concept as consistently sticking to a schedule where you would need to practice every day for roughly the same amount of time-- as long as that part is being done, there would be consistency in adding/reviewing and time required each day, and it might be more fun to trickle words in consistently so things stay consistently fresh versus having days where new things are added and review-only days. (The point is to have fun, besides just learning, after all)! You could however decide to disable automatic word adding to have complete control over when you’d like to see a new word, so new words would only get added when you press the (+) manual word adding button.
Here’s a link to a doc on the scheduling system which should help get a better sense of what’s going on and how to study accordingly: http://docs.skritter.com/article/51-spaced-repetition
Since originally posting this, I’ve given it substantial thought, and I see that it isn’t easy. I haven’t auto-added words for a long time now, and that works much better. Now, I add 5 words most days, occasionally 10, and sometimes I don’t add words for a day or three if I’m too busy or just not motivated enough, and as manually adding is trivial, there really is no overhead.
I’ve come to realize that, for me, the challenges start when I have 10+ words in the pipeline that I don’t know, that really drains on my motivation and takes a lot of effort. As I don’t really have energy for this effort on a daily basis, that quickly spins out of control, and suddenly I find myself with hundreds of words to practise, which is too much.
IIRC, while auto-adding, and not having gotten down to zero words on a given day, those words that would have been added that day accumulate, so that if you’re auto-adding 5/day, if you only get down to zero on the third day, you get 15. If this is the case, I think it’s problematic, but I might remember wrongly, feel free to clear this up.
I have one suggestion here that might be able to help learners like me, that if Skritter notices that you are growing the number of new characters you fail to remember, it can prompt you whether you want to switch to manually adding (possibly for a while). That might help you avoid sliding too far.
Aaaand that’s brilliant. 
As with any SRS, a growing queue can be an issue when studying isn’t consistent and things are added too quickly. It would be extremely handy if Skritter detected this, gave you a heads up, and a way rectify the situation.