I miss a feature where I can put a minimum percentage where items will not show if they are under this percentage. Like 80% or something.

When I have had more time to study a few days in a row I hit this level, and then I would like for Skritter to only start adding new items instead of asking on items that are not due yet. Possible?

I think the simplest way is to manually add words when the % gets below what you are comfortable with. If you know you are going to finish your review queue and add a lot of new words during a review session it makes sense to add words manually a bit earlier (Skritter doesn't add words when you have a long review queue but if you know you are going to clear it and add new words adding them early helps you to review them more times during the initial practice session).

Adding in the beginning when knowing that I will finish the queue is a good idea, I'll start doing that.

Adding them in the end feels a bit like an unnecessary click for every item though. I do think that it should be possible to automatically make Skritter not ask about items that are not due. Which it says itself (ie "79%, not due").

http://www.skritter.com/account/settings-language

Increase "Add Word Frequency"

But as I understand that function, it doesn't really work the way I mean. I don't want words to be added more frequently when I have lots of things to review, only when I've only got items <80% ready to review. Of course I could set it differently when I reach that level, but I like the computer to do as much work as possible for me... :)

Anyhow, it's not a big deal, it's a very insignificant function in the whole, but couldn't help bringing it up.

If you increase that option, it will start to add words a little earlier, when you have a few more reviews due. But in most cases, the largest effect you should see is that it adds a lot more words as you get down past 100%, so that you don't hit <80% as much. Give it a try and see if it does what you want.

OK, thanks for the info Nick, I'll give it a try!