Hiya I joined weight watchers in June 2011 after a particularly bad series of GP visits. I had tried slimming clubs before and they all worked whilst I went but the weight came back as soon as my enthusiasm waned. Its very important whatever you do to be going for the right reasons - that you want to lose weight for you and your health, not to be slim for an event or to fit into that special outfit (although those are fine as short term challenges)
Weight watchers have changed their approach over the last year and this has been made very obvious in the last week, as they have completly made over the online and meeting tools to reflect a new philosephy (based on research, not just marketing hype) of permanant weight loss. The plan is much more about looking at your habits and behaviours and how these need to change for long term success.
I love going to my meeting, even when I have had a bad week and gained weight, I usually can identify where i went off track so I dont go throwing myself in the nearest box of pringles!! I am not a fast loser, but I reason that I didnt put it on overnight and I need to adjust my habits over time too. Somebody who met me recently ridiculed the fact I go to WW saying "what do you need to go for, you are skinny" It was the best complement anyone has paid me about my appearance for ages
I had to explain to her that last year I was 50 pounds heavier and four dress sizes bigger - she wouldn't believe me 
Group leaders are differant so, although you will hopefully like the class you join and acheive a great loss, if you dont like the first class, you can always try other ones in the area.
Hope it all goes well for you 