Five weeks in, and haven't slipped once. After years of dieting, I know that (for me) one slip is the slippery slope to more slips, and ultimately to giving up the diet, so I don't allow myself any slips at all. I want to get the total food replacement stage out of the way once and for all, so it doesn't make sense to delay its completion by eating off-plan.
I have had one meal out in that time, for which I developed a plan in advance (and stuck to it). And I had a small amount of smoked salmon at a function where it would have caused offence not to have taken something that was offered to me. But both of those were in my fourth week, when I was supposed to be adding extra food each day, and they were in accordance with a predetermined plan and within the Low Calorie Week limits, so they do not count as slips.
Twice, though, I have forgotten (or simply not had time) to have my third pack of the day. Which is suppose is a sort of slip.
There are slips and there are slips, though. Bear in mind that Working Solution (adding a low-carb 400-cal meal each day) is a valid alternative to Total Solution, and there is only a small difference in average weight loss. A slip may not have a huge effect on weight loss either, but for me it has a knock-on effect on my motivation and determination. If I allow one slip, what is to stop me from allowing another, and another, and another?