Memrise (under the languages section) is pretty amazing. Or, at least seems amazing from 15 minutes of going through the Chinese stuff. I hate memorizing things, but the interface and visual cues for learning characters, and way they track your progress actually makes the process enjoyable for me.
So far, at least.
As with all these tools, you could teach yourself this stuff before, it'd just require more work and discipline for you to find the necessary books and make your own teaching plan. The advantage of these services is that they lower the friction to learn. Hopefully they reduce the friction enough so that there is a much higher ratio of enjoyment/reward to effort, making you more likely to stick with it. But you still have to stick with it to learn anything.
Seconding Skritter, they're amazing. I'd also like to add that they support Japanese kanji as well, and that their iOS apps are brilliant. The Chinese iOS app is out, and the Japanese one is in beta. I own a Wacom tablet that works great with the website, but more and more I find myself using the mobile app because it feels even more natural than writing with a pen, and I can do it anywhere.
Skritter seems pretty sweet, but has no love for Cantonese; it supports traditional characters (so they're most of the way there), but the tone selection is mandarin-only and they only display pinyin and not some cantonese phoneticization like jyutping.
I'm doing some Memrise now and the best thing about it is they seem to have gamified it. The plantlings that grow really do encourage me to keep, well, playing.
I find that when there's a secondary motive to keep going with a task, like the plantlings you've mentioned, that I'm actually not properly completing the task in question. I'm not learning the language as best I could because I've also got my mind on making the plantlings grow.
To get the very best out of your time for any task you should only have one motive to do it: because you want to.
I'm a big fan of Memrise. I think one of the best features is that it uses the community to suggest ways of remembering a word. People remember things differently, so if you have to see a picture of a baby crying with his mouth open to remember that the word 口 means mouth, then so be it.
I'm hoping duolingo comes out with their Chinese track soon. That'll be very interesting.
I'm not a huge fan of Memrise, especially for Chinese. At least when I checked it, there was way too much of an initial emphasis on characters and it also suggested a widely-believed but incorrect idea that characters = words. I say this as someone who has spent most his adult life in the Chinese speaking world, gone through the struggle of learning myself and met hundreds of other foreigners doing the same.
The best option for learning Mandarin would be Popup Chinese. If you exhaust their materials or find yourself wanting a southern accent, go on to ChinesePod. Once you can already speak and read some, go to Skritter if you want to learn how to write. If I had had these three resources 10 years ago, it would have been a much, much easier path.
Duolingo is attempting to do the same "gameification" of language learning that Memrise is doing. They're both fairly successful, but I find that neither of them are as "sticky" as a really good game. It's too easy to put it down.
I was learning French with Memrise for a while, but found that after a certain point the memory keys were...not great. I've not been back for a while though so might give it another try.
I agree this will be the problem with service-like spaced repetition software like Memrise. They will start off with beginner examples and then totally drop off once you transition into intermediate.
My opinion is that SRS must be ingrained with your own interests. Additionally, the base decks on Memrise don't use further flash card techniques other than Q/A or word/definition. Cloze deletion cards come to mind when memorizing things much easier.
This is one of the problems. The framework is good, but content usually isn't. Content in SRS is really hard because language learning should collide with interests in order to feed the fuel.
More dedicated SRS users will just move to something more portable to create their content more easily/personally and beginners eventually drop off.
So far, at least.
As with all these tools, you could teach yourself this stuff before, it'd just require more work and discipline for you to find the necessary books and make your own teaching plan. The advantage of these services is that they lower the friction to learn. Hopefully they reduce the friction enough so that there is a much higher ratio of enjoyment/reward to effort, making you more likely to stick with it. But you still have to stick with it to learn anything.
Here's hoping I will.