I have had one of these almost since I got my 10D. I don't use it as much as my 28-135 which was recently retired by 24-105is L. However, I reach for this at weddings and whenever I am doing portraits. For the money it is unbeatable. A friend of mine was all set to go out and buy the canon 2.8 L but borrowed this one and bought one the next day. He is gradally replacing all his low end glass with L pieces as am I, but doesn't feel any need to replace this one.
His unit is very quiet, comparable to a USM. Mine is a cement mixer, which is why I don't use it as much as I might otherwise.
The comparable canon glass focuses faster, but I don't think it shoots substatially better. Now if canon would come out with an IS version, I would rush out and buy it. Till then, the only chnage is that I might seek a quieter version of the same piece.