Its not very hard to paraphrase an answer, and if you actually read and understood the source, to actually add something to it.
I think the academic way of quoting (well sans citations) is a pretty good way to go about it.
Firstly - essential information needs to be in the answer, and where necessary, explained for the target audience - in this case, while essentially, the answer is adapted from lifehacker, I've explained the switches they have used (which they hadn't).
If you're copy/pasting large chunks of something where there's more than one way to do it, something is off, especially if spelling errors carry over. My way is to quite literally write everything in my own words. I've got a lot of practice from doing that in school :).
At the end, an answer has to be reasonably original, self contained and link back to sources if users need to look up additional information. It shouldn't rely on a link as an essential part of the answer.
In the example given in Kronos' question I couldn't actually tell where the answer could be, and I felt it missed the crux of the question - the user seemed to want to do a scriptable use of the mail command as part of a shell script, as opposed to use it manually - the section that was relevant eventually needed the use of the control-d key combination to send the mail, which wouldn't have used.
I think understanding the question you're answering is key in this case. Then you'll end up writing a naturally good answer. Unfortunately this is pretty difficult to do, without seriously extensive edits for link only answers.