From their post:
Have you ever wanted to write something and get help correcting it? Now you can write a short post in your Notebook, and get other italki members to correct and comment on it.They kind of make it sound like they're doing something completely new, huh?
Their system is fairly straight-forward, where the text is copied to a comment window below and you can format it to show your corrections. Their correction interface isn't quite as good as Lang-8's, but I certainly can't complain about having yet another place to get my writing corrected for free.
Update: After putting up this post, I got an email from Kevin Chen, one of the founders of italki, who shed some light on the development of this feature:
You're right that the corrections feature is nothing very "new" --- honestly, it was on our to-do list as early as when Livemocha came out way back in 2007. For a while we watched people use our answers and group sections to get corrections. However, the real answer is that we just got carried away with other priorities (our marketplace). At this point, the corrections feature is anything but "new", and every language learning social network has this feature, including Livemocha, Busuu and of course, Lang-8 (which I think is great). That being said, it is a really useful service for our users, and we think it deserved its own heading at italki.The only thing I'd note is that I disagree that Livemocha and Busuu really have this feature. As I've noted before, on both of those, you can get text edited, but the text you're submitting is supposed to be the assignments of the courses on those sites, with prompts like "Describe six objects...", etc. Before italki entered the ring, Lang-8's only true competition in the free, write-whatever-you-want text correction area was CorrectMyText, which hasn't gained quite the traction of Lang-8.
Feature: Write in your Notebook and get corrections [official italki blog]
Get your foreign-language writing corrected online for free [Street-Smart Language Learning]