To the folks recommending Nova and/or reduced animation settings, I don't think that's what folks are complaint about whether they say "lag". Nova is faster, but in part for the same reason as reducing animation in Dev settings, it spends less time prettily transitioning screen to screen. That makes the transitions faster (though less visually "smooth").
But it does not help when the phone takes a sporadic extra half second breather unlocking, or bringing up Home, or starting the camera, or skips a frame every once in a while. I think that's what people mean when they say" lag".
Many don't notice it because they're not looking for it -- I envy them -- but once you see it, sadly you can't un-see. :-\
PS. I'm still running pre-VZ patch, since I haven't quite decided to give up on getting root/ROMs in the future, so can't comment on the improvements many have praised with the update. Given the breath and duration of the comments, it seems to go beyond the usual placebo effect of updates, but it's suspicious that VZ's official change log makes no claims about speed/smoothness/responsiveness gains of the update.
I know what you mean regarding the update, for what it's worth, I have not updated either, but I'm also running CleanROM, so that may be part of the reason I don't notice any lag either.
Having said that though, I wish I could find the one youtube vid I watched a while back regarding the animation options set in the developer mode settings...they were actually able to reproduce the common lag issues you speak of (extra half second breather unlocking, or bringing up Home, or starting the camera, or skips a frame every once in a while), and demonstrated that setting the transition animations to zero did basically get rid of it. So yes, changing the setting does remove those "smooth" transitions, but it seems like often it is these transitions that ARE the source of the lag (though definitely not in *all* cases), so eliminating them is also a potential solution to the problem.
Regarding the use of different launcher, it seems the same thing is true, as the lag really seems to be tied to Touchwiz itself, so using a launcher like Nova seems to improve the experience for many.
Again, I'm really just sharing information I've come across here. Of the two suggestions I made, both are easy to do, don't cost anything or even require root, and completely reversible, so it seems to me like they're worth trying.