Ever since I started using Skritter on my iPad, I've found that I am way more than caught up in my review queue. So, I'm a little concerned about getting to words that are "not yet due" - i.e. < 80%. What does it mean exactly when a word is "not yet due"? Would it screw up the SRS algorithm if I reviewed words that weren't yet due? Should I speed up the word add frequency (or add more words manually)? I have it on "normal" with 95% retention. Thanks!

They tend to refer to it as overpractising, and it shouldn't mess anything up, you just are practising things well before you'd forget them: imagining 100% is just when you need to review it, so 80% is just reinforcing it sooner, thus pushing back the next review. That's my understanding at least.

As far as I know that it should be adding words pretty frequently if you have completely cleared your reviews, because even the 'slow' setting would be adding them then. If you're being too ninja with reviews then maybe kick it up a notch with the button that lets you manually add a whole bunch at a time. The FAQ warns against going too overboard though http://www.skritter.com/faq#more_words .

Aaanyway, based on your stats you're pretty advanced so your learning process might be different from mine; maybe someone more experienced can weigh in.

It doesn't screw up the algorithm; the algorithm adjusts and doesn't push the item back as far as if you had studied it on time (and conversely, items get pushed back proportionally more if you study them when they're way overdue, and you get them right anyway). But generally speaking you get the most efficiency if you study things right when they're due, so I'd suggest upping your adding rate.