I have seen several negative comments about the eight 10-minute takes and three fade cuts that comprise this film, and many of them seem to miss the point. For example, bob the moo said, "but I don't understand why he didn't just accept that he would have to make do with 10 [actually, eight] different shots instead of trying to hide the edit. Each time he does it by zooming in on a black jacket and then pulling out again after the edit."
The whole idea was to build the suspense and make the action appear to take place in "real time" by not having the camera appear to blink. Thus the 10-minute takes (and three fade cuts at approximately 20-minute intervals); and I think it works very well. It also makes one appreciate the excellence of the acting. It is extremely difficult for actors to execute a film flawlessly in only eight 10-minute takes, and the three principal actors did a fantastic job under very stressful circumstances.
I think the reason the film was not a big box-office success is that people were expecting the usual Hitchcock action (think of earlier Hitchcock films such as Saboteur, Foreign Correspondent, The 39 Steps or The Man Who Knew Too Much). But any serious film buff should not miss this film.