I'm of the opinion that the random disconnected order that words appear in is both Skritter's biggest downside, and spaced repetition's biggest too. I'm going to suggest that some grouping of words by list is necessary for good recall in both Skritter and real life, and will lead to more efficient practise. Bear with me!
A problem with spaced repetition is that while sometimes words do get grouped together by virtue of being added together, for the most part they show randomly and you're left wracking your brain trying to figure out exactly what needs to be written. In terms of speed, this is slow, and I think not optimal for recalling either.
I tend to find that language is learnt best by making associations. For example, one day studying the word for "wardrobe" 衣柜, and a few weeks later the word for bedside cabinet 床头柜 is not as efficient as studying them together, being reminded of the links between them, and the differences. Especially when you come across a word which is similar, but not quite, and leaves you confused.
Now, the Skritter guys have done some great work recently to help us out here, including custom definitions, seeing list names, mnemonics and the star system (to highlight words you don't know). They're also wanting to include example sentences. This is all great, but words will still be thrown at you randomly.
I believe that if you have the words for wardrobe, and the word for bedside cabinet coming up together, this will reinforce recall. In and outside Skritter. Other than having taught language in the past, I've no great academic qualifications here, but I don't think it's that contentious.
My proposal is that while spaced repetition should of course remain, it needs to be supplemented by a more natural grouping of words. I hope this can be done without too much heartache.
I could see it work this way: Skritter should not only take into account grouping words by reading, writing, or spaced repetition, ***but also by being in a common list***.
Beside cabinet and wardrobe are in the same list. If on Thursday one should show up with "2 weeks since last seen" and on Sunday the other shows up, also with "2 weeks last seen" then they should appear both together, one after the other on Thursday. For words in the same list with a 12 hour difference, instead of 1pm and 3pm, put them immediately together at 1pm. Words separated by big time differences remained separated, but the closer ones in the same list get bunched together.
If this is done on a large scale, you will find that you will be able to get through reviews quicker, not constantly wracking your brain, and by association they will help your recall, and by seeing them side to side you will get less confused by similar but different words.
I hope I've made some way into convincing you here. I've been having a lot of trouble with the tremendous amount of vocab I've added, and I think this is the best way to deal with things.
In the long term, if this is implemented, I'd also like to be able to go through all the words I've added, and stick them retrospectively into lists, while allowing you to prune words you no longer want (instead of using the 'delete all' button which is far too extreme), but that would be more of an undertaking.
And er, thanks for reading!