Does it matter? To me it does. When I'm trying to read something technical and I come across errors in spelling and grammar (non-technical errors), it throws my concentration out the window. I'm not claiming to be an expert in the rules and spelling of the English language (or any language) and although you'll find errors in my writing, I do try and I do care.
I try to read as much as I can, and I particularly like books. In the computer field there are particular publishers, everyone in this field knows who they are, and everyone has their favourites. There's one in particular, unfortunately, who seems to do quite a bad job of editing. Their books seem to have higher-than-normal levels of non-technical errors making their books difficult for me to read. Some of their books are fine, which leads me to believe that most of the editing is left to the author, and we're simply observing her/his mastery of both the technical topic at hand, as well as the English language.
So I was quite pleased when this particular publisher got in touch with me last year to ask if I'd be interested in being a reviewer for some books that were in the process of being written. Here was my chance to not only review the technical details of a book, but to also try to make sure all the non-technical stuff was good too. Therefore, initially, I said "yes".
Then they sent me an email describing how to be a reviewer for them. One of the very first instructions clearly stated that my job was to review the technical aspects of the material and barred me from making any suggestions or corrections to any non-technical aspects of the book. So I then changed my mind and said "no". Looking at some of their publications, I wouldn't want someone to see my name as a "reviewer" and wonder how I didn't notice so many obvious mistakes!
This same publisher had a sale recently, so for a very cheap price I purchased a couple ebooks from them, one of which had not yet been published. I figured for such a low price I could take the risk they were poorly written and hope to glean any nuggets of technical information despite the distractions. The book was published the other day, and in what I see as a very ironic twist, they sent me the following email to inform me of the change in status:
PS I hope this post doesn't dissuade a technical person (perhaps a non-native speaker of the English language) from writing. I'm not trying to poke fun at peoples' language abilities. But as a publisher of books in the English language I think there's a higher standard to which the publisher needs to be held!