I've bought the 24 f 1.8 only yesterday, but judging from the handling and the first images, I am quite pleased. From f 2.8 upwards, the images are very good; the bokeh is nice.
On my 20 D, this lens has the potential to turn into my low-light lens of choice.
However, the fact that something seems to be lose inside the lens when you move the camera-lens combination to and fro is very irritating.
And yes, its rather big and heavy for a prime wide-angle, but I don't mind, being big and heavy myself ;-).