It varies quite a lot from person to person, I usually notice around the time group members are getting to their Club 10 though, I honestly do, I can usually tell when someone is getting near to that award ~ I do the weigh-ins at my group mind you, so I'm seeing people every week standing on the scales!
I think it's great seeing people achieve their goals, bit by bit, week by week, month by month! The look on people's faces can say it all! Sometimes the number on the scales doesn't actually co-incide with when you notice the difference either! The difference can just as easily be in the person's self-confidence, and attitude ...... a new, more flattering, modern hairdo, a bit of lippy, or a new colour of eye-shaddow .... they just feel so much better, and actually WANT to look their best!
However, I'd say that every 1/2lb counts! It all adds up! I used to keep trying on clothes I had in the wardrobe, the next size down, looking back at any "before" pictures I could find, looking in the mirror, taking my measurements .... all those things can really help to boost you along your weightloss journey road! Best o'luck'n'stuff! Stick with the plan, and you WILL get there!