We used it last year and honestly, I wasn't impressed. I used it with 4th and 7th graders. Can't really tell you what I didn't like about it, it just wasn't our style, I guess. I know there are some people here that really like it, though.
I have it, and we've kinda started on it, but we're not really going to get into it on a regular basis until the Spring semester. I can't really comment yet. Looks good from what I've seen, but I don't know yet if it's our style.
I've tried it, three times, with two different kids. As much as I like it, it's just not a good fit for my kids. My oldest is using IEW and so far doing well with it. Not sure what I'm going to do with my middle, IEW is a little more involved than he can handle right now.
I've used level 3 once before, with a small group of 9th graders who had not had much in the way of writing instruction prior to that. Since I only had one copy and 4 kids, I had to *teach* it, in modified fashion instead of letting them share the book. At first they weren't in favor, but as we progressed, they enjoyed it more, and actually turned out some pretty good pieces by the time we finished it. Not what I'd call 9th grade level, since of course it was only level 3, but it did get them over their "fear of blank paper". I may actually try it again at some point in the future...
I have it for my DD11 who isn't much for writing. We are comming from a program that talked about different ways of writing but didnt have any assignements for more practice. Now that we have completed that program I will be using WS a bit more regulary. I am starting with Level 3 and my DD is moving rather quickly with it. She seems to be enjoying the program and it's geared to self taught so I just need to review it when she is done. Then we type up her final paper and email it to Dad who has the final say on the paper on rather it's good or bad. So far she's done well with little grammical/spelling errors. I plan to start Level 4 in January.
I used Level 1 and thought it was a good introduction to the creative writing process. I considered other levels, but went another direction.