0.5lb a week is 26lb in a year - nearly 2 stone
1lb a week is 52lb a year - about 3.5 stone
1.5 lb a week is 78lbs a year - about 5.5 stone
2lbs a week is 104 lbs a year - about 7 stone
every little helps. You will have good days and bad days, but you have to play the long game. If you want super fast results without the work, then a different diet might work better for you. But ultimately, WW is most likely, IMHO, to result in sustained weight loss as it teaches you portion control and self restraint, whereas other diets seem based on "eat as much of X as you want" or "only eat this product, nothing else" - neither of which will reprogramme you to eat in the real world.
My advice is always this....one or two days of shovelling anything in the fridge into your mouth does not herald the end of your diet. It gives you an opportunity to assess WHY you needed to snarf a packet of biscuits and look at the emotional triggers for your eating. Then, you pick yourself up, dust yourself off, get back on track and face the music on WI day. And start again.
Id also say set realistic goals....I d love to say I would be able to get 5.5 stone by my one year point, but realistically, that is not going to happen. Im currently 14st 6lbs
My goals are
short term: to get to the 2 stone mark in the next 2 weeks by losing 2lbs and not sabotaging myself.
Mid term: to get to 13st by Easter. (down 1st 6lbs)
Long term: to get to 12st by june 13th. This will mean a 4st weight loss in total over 1 year.
Very long term: 10st 7lb by Christmas.
Gawd, it looks like a blaster ticker..... 
If I don't manage it, well, as long as Im still heading in the right direction, thats OK. I fully expect to plateaux at some point - like I did from September through November.