duolingo finally releases a Japanese course:
https://www.duolingo.com/course/ja/en/Learn-Japanese-Online

I think I'm going to give it a try.  If nothing else, just to try to stop me from forgetting Japanese completely.

I'm worried that my Japanese has become very rusty in the 7 years since I left the country.  (Wow! That long already.  How time flies!)

I've already been using duolingo to study Vietnamese.

From listening to podcasts like TEFLology, I'm well aware that professional linguists view duolingo with disdain.
And yet, for all its shortcomings, I still find it fun.  (I'm a sucker for all the points and rewards systems.)
And at the very least, it's better than not studying at all.

Anyway, if you're on duolingo, look me up, and we can compete for weekly points.

https://www.duolingo.com/JoelSwagman

Update:
I've been working my way through the Hiragana exercises.  (I know Hiragana, but because I'm anal about these types of things, I decided to start all the way at the first level and work my way up.)
It's a good idea to get Japanese learners into Hiragana as soon as possible.
But, in my own experience, one of my biggest problems learning Japanese is that I learned the Hiragana characters as being equivalent to Western letters.  And so I pronounced them like English letters, instead of with the Japanese sounds.  Once I got into this habit, it was very hard to get out of.  (My biggest problem was with the Japanese liquid sound).
I think it may be a mistake to have learners match Hiragana to Western letters.  Duolingo should instead have learners match Hiragana symbols to sounds.