It might be cool to give people a discount if they make no or only a few mistakes. It seems like some people don´t even read their posts before they submit them (especially on Lang-8…) while others put a lot of work into their submissions. Both groups of people pay the same amount of points, which is unfair towards tutors and serious students.
I have used Lang-8 and was pretty happy over all with the results. At the moment, I don’t like writing just for the sake of writing but would like to find a pen pal who is close to my level in the language I’m tying to learn. A mid level beginner.
The problem with Lang-8 was as Colin mentioned some texts were very easy to correct and selfishly I would seek these out and avoid the really tough mangled ones. I would correct one for every submission I sent out. My problem in the past was trying to express concepts and ideas which where way beyond my ability and I relied on Google translate for most of the work.
I think the right way to go about it is to try to write at your level, about familiar subjects and use a dictionary for spelling and to find the correct gender etc. IMO I think the over 90 percent of the corrections at lang-8 are good enough, even natives don’t have perfect grammar, that’s not the point. I just want it to be corrected so it seems natural, and have the obvious mistakes corrected. I don’t care that much about nit-picky stuff. I to have myself seen spelling errors in the past that weren’t correct but to me that’s not a big deal.
For me, the corrections are not so vital. I want to know if what I have written is correct, and I like to try to figure out quickly what I did wrong, but I don’t spend more than a minute or two looking at the corrections. For me, the main thing is what I have learned while writing the text.
I learn more about grammar and natural language by searching for example sentences at linguee.fr than I do from getting corrections.
Google is useful for this, too. If you’re not sure if your phrase is correct, just google it. Type the phrase into Google and you’ll probably get a correct phrase back. I even do this for English when I’m writing essays for school.
“The problem with Lang-8 was as Colin mentioned some texts were very easy to correct and selfishly I would seek these out and avoid the really tough mangled ones.”
I don’t really think that’s selfish.
You’ve got to learn what sort of texts people are willing to correct, not force yourself/others to correct difficult posts. I mean, it’s a free service and people aren’t obligated in any way to give corrections.
I’ve often started correcting a post, then realized I had no sweet clue what they were trying to say with a certain sentence, didn’t know how to help them and gave up. That’s not really the corrector’s fault… especially if the writer didn’t include a native language version.
It’s the same with overly long posts. I’ve had a guy literally post a novel, then complain that no one corrected it and asked me to… for absolutely no reward whatsoever, of course, because Lang-8 is free. No one’s going to correct your novel for free, that’s not how society works…
Also – I agree with the awesomeness of Google. 
When correcting on Lang-8, I often came across nonsense sentences that I could not correct. Normally I would continue going through the text, but I would just write on that sentence that I don’t understand it and ask if they would explain it. Lang-8 is certainly not the place to get long texts corrected. I would say 500 words is a reasonable limit.
What I didn’t like was when I would post corrections for an English text, and then somebody else would also post their corrections for the same text. Not once did anybody disagree with my corrections, so I have no idea why they would do that. It is of course better to have several corrections than one, but given the number of people waiting for their English texts to be corrected, this should not be a priority.
“Lang-8 is certainly not the place to get long texts corrected. I would say 500 words is a reasonable limit.”
500 words is a pretty long text and I’ve noticed ones close to this long tend to get ignored. I think people are much smarter to write in chunks like 100-200 word texts, so it’s more likely to get corrected. The only problem with including your native language with the text is pretty much every text I corrected had Japanese or something similar as there native test, which I don’t understand.
Luckily for me, I’m learning German and most Germans I submitted posts to understood English and some gave very detailed helpful suggestions. However this was earlier this year and I made minor mistakes not like when I started, which would be pretty rough if not impossible to correct without the native understanding English, along with my submitted translation of the mangled post.