I'll "weigh in"
I am in my 7th week of OPT. I weigh myself every day. I lost the most weight my first and second weeks and since then it's been a lot slower...but, as Leigh talks about it in the FLTS - the overall TREND is that I'm losing. I'm 9 lbs down after starting OPT on March 4th. My clothes are much looser (some don't even fit anymore) and friends and family are noticing. But, yes, it's half a lb up one day then down and sometimes I stay at the same weight for days at a time. This is the first thing that's really worked for me in YEARS -and it's actually fun and doable!
For me, after the 4th week (the rest week where you calories are low and protein intake is really high) is really when I hit my stride and it started becoming second nature. Stick with it and you will be pleased, believe me. I had tried what felt like EVERYTHING until this!