I have been using WebCape as a placement as well as an assessment tool in Intermediate French for the past two years. The students take it during the first week of the semester (the minimum to enroll in 2nd year is 300) then at the end of the semester before the final exam. In many cases the test will show a difference of as much as 60-75 points for a 5 hour/week semester course. In students who take less than 5 hours of French per week, the score will increase by 30-60.
Students take the test in the language lab and have their scores sent to them and to me by email or they bring a printed copy of their results to me. They take it when they return after winter or summer break even if they have taken it at the end of the previous semester because there is usually a slight difference after the students have not been exposed to the language for several weeks.
WebCape appears to be an excellent assessment tool, not only for the students themselves who can keep track of their progress, but for instructors as well who can use it to evaluate their teaching effectiveness.
I have seen a few puzzling cases in which the scores did not at all reflect a student's proficiency either by being too low or too high. But these are exceptions and in general I find that the test gives a quantitative equivalent of what an oral proficiency interview would tell me about a student's level.