I feel like life would be strange if I did not have Midori in it. Together with Jisho.org it makes up pretty much 100% of my Japanese reference tools. The more you put in the more you get out. If you are just starting to learn Japanese, I really recommend dishing out the cash for it.
My favorite features:
--Handwriting recognition: if youre reading or you see a kanji you dont know while walking around in Japan, simply open up Midori and draw it in. Then bookmark it for later.
--Bookmarks: Midori has a really nice bookmark capabilities, allowing you to create folders and subfolders. It greatly helped me during my intermediate Japanese lessons in college. I created a folder for each lesson and two subfolders inside of that; one for kanji and one for vocabulary. Thats great in and of itself, but its even better knowing that you can make...
--Flashcards: perhaps a little underspoken is Midoris flashcard capabilities. You can make a set of flashcards at any time out of any of your bookmark sets. You can customize it by showing back or front first, hiding readings... Its great for anyone whos going to be tested.
--Lists: Midoris got a bunch of handy built in lists, especially for beginners. You can learn hiragana and katana right from within Midori via flashcards, and Im currently using it to study JLPT N2 kanji. The parts of speech lists is great to browse, too.
--Notes: You can make notes on anything you look up to remind you of where you found it or why you wanted to remember it. Also for if Midoris definition happens to be a little off, or you want to add another contextual meaning etc.
Things that need work:
Midoris built-in translator isnt going to translate sentences for you. It mostly plucks the kanji out of the sentence and gives you their readings and meanings. Not so helpful when you dont know the grammar for the sentence. Hopefully theyll implement one that busts Google Translate in the chops. On the plus side, you can copy an entire newspaper article and get a kanji list generated for you that you can make flashcards out of.
No kanji stroke practice: This is a little unfair to pin on Midori, as there are very few apps on the market that do this, but I would very much love to see a function that allows you to study kanji by drawing them to see if theyre right, trace them to memorize them, that sort of thing. Midoris already got the handwriting recognition, would need only to incorporate a system that uses it for review and study instead of only searching.