mpenza, the only practicality I see in using the 12-24 is for group shots, that's about it for me, personally, I t-loaned the AF-S 12-24 for my that wedding shoot was to get the group shots in & nice, being wide at 18mm, I found that I can go close and not worry about backup towards the walls/pillars of the dining areas.
But I definitely lost my range & the urgency for upclose & personal shots if the need arises.
Like what Watcher mentions, it depends on your style & the way you want to shoot, but I think more importantly, is how the couple wants their shots taken. A slight tilt of the camera will cause distortions if you're not careful although the couple & viewers might not take note, but as a photographer it hurts me slightly if I do see perspective distortions.
All I can say is that the 12-24 (FLM - 18-36) is not for the faint of heart. The 17-35 would be wide on film, very wide, I've already tested an 18-35 on a film body, but scary, the distortions are very scary. Try it only if your heart can take it. And as mentioned, there isn't really any need for any wides to go below 28mm, even for weddings.
Also, I'll have to say this even as I know Watcher is going to slap me at the next Nikon Council :sweat: . The 12-24 was *originally* intended as a landscape len, even if I do zoom to 24 (FLM 36) I won't find it comfortable for personal & portrait shots. I want to blend in with the happiness of the couple, they shouldn't not remember I'm there but at the same time I should get my shot. 12-24 is only feasible if you have the couple's attention and you can afford the wideness. Any len can be used, but the results will depend on still the photographer & the characteristics of the len (thanks to the pro who taught me this).
The best & ideal lens for Nikon users would be the AF-S 28-70 f/2.8D, it covers the best range you'll need, but alas... the 28 becomes a 42 FOV upon on a digital body
And yes, if i'm shooting film for weddings, I promise you, the 17/18-35 will not be affixed on the film body, rather the 28-70 (ok ok I'm dreaming that I have these lenses ;p ). But if on digital body, give me the 17/18-35 any time (FLM 25.5/27-52.5). 12-24 is usable, but it boils down to your preference, and as I go back to my practicality mention to mpenza in my starting statement, that's all the 12-24 does for me. That's all folks ;p