I'm eye-ing this lens for a while, have to wait because of the money (have to save for it) and because of the reviews that says we dont need it, its too heavy, could do the job with F4 version, etc, etc, etc....
One day I have enough money to get it, plus there was rebate program ($100) and my brain also wasn't in 100% normal working condition, so I "accidentally" click the "submit order" button and there you go, I've bought it....
Used it for the first time at the wedding, and yeah, people were right, it was too heavy, after just an hour holding it, my left hand becomes so shaky, but I got great result on that day though...
So, conclusion, it gives great result, but weight is a little bit of an issue for me.
Used it again for second time at different wedding, this time prepared better than the last one.
I was able to get even better result than the last time and my hand is not to tired anymore.
BTW, I also have the F4 non IS version and love it too because of the result and the lightweight, but the F2.8 IS is more preferable because it looks better (more "real PRO" like), image quality (I love both result from F4 and F2.8 IS), bokeh and lower light capability when needed OR in my case I can use my F4 if the wedding is outdoor and use the F2.8 IS if its indoor.
Conclusion, I have no regret buying it.
I love the lens, I love the result, I'm happy with it.