I have de 17-40 and i love it!!


I've haven't had (yet) the opportunity of testing it in weddings, how ever i recently shot in a concert and it did work very well for me even though the low light conditions.
I guess it isn't ideal depending on how you work, using a 50D + 3200 iso + 1/50 (in the "backstage" without spotlights before the presentation) and the work came out pretty good i think, i did edit them, bring up light and noise reduction.
I think you can manage it without a flash, however it does require a little extra time editing, using bursts if you use really slow speeds, and of course if you don't mind too much about noise or a little loss of quality in the images. How ever i think it also depends on where and how will you be using the pictures. Most of my clients won't make very large prints, or watch the pictures at 100% in their computers, so i don't think it's a reeeeeeaal problem the noise thing.
You can see the pictures here in case you want to see some samples:
http://www.facebook.com …100001695671439&aid=22991
I don't know if the album is public however 
BTW i've never had any problems using flash in churches at weddings so i'm not that worried about flash, and i think most of the times i find some where to bounce the flash, so i don't worry too much about the F4 any more, i think it's all about finding some kind of "cheat" to make up the lack of fast lenses 