This is what I keep hearing from folks at some of the clubs I visit.
I have the 24mm f/2.8 IS and it is a stellar lens. The image rivals my 24mm f/1.4 L II easily and for video on a stabilizer it is second to none for Canon video enabled DSLR bodies. It has relegated the 24 L II to night time time lapse and and low light HDR work.
If I was using full frame mostly, I'd jump on that 28mm IS in a second. The image quality is simply incredible if my experience with the 24mm IS is anything to go by.
I tried to resist but went ahead & picked one up. Already got confirmation that its packed & ready to ship.
I wasn't going to buy it since I'd rather try out the 24mm is. But after looking up the used prices for this lens, I figured (justified?) that I could play with it for a few months (or a year or so) & then sell it for a small profit.
If there turns out to be a problem with the lens, or the order gets cancelled or something, I'll come back & post. That way everyone that resisted can say thank god, or "Yeah, knew it was too good to be true". Or maybe, "HA! You get what you pay for!!"...