After having tried the 50mm f1.8 for a few weeks, I have decided to get the 50mm f1.4 for its superior image quality, its decent focus ring (compared to the f1.8) and the USM. This lens is sharp wide open and the softness that many will experience is quite probably due to mis-focusing. Focusing is indeed inconsistent with my EOS 350D (it can hunt wildly for a few seconds in low light), while it is spot on with my EOS 1N.
Construction-wise, the lens feels very cheap for its price (and especially when compared to an old FD 50mm f1.8). It is surprising light compared to my other lenses (135mm L and 17-40L). I was disappointed by the cheep feeling of the focus ring. It is far from being as smooth as on my other lenses. All this said, it does its job correctly and focusing is much easier than on the 50mm f1.8.
All in all, it is a great lens optically (as I have said, sharp from f1.4, but you will see some CA and sometimes halation at this aperture), but it would be nice if it had the construction of the other non-L USM lenses.
Oh, and there is no lens hood included. Since the lens is prone to flare, this accessory is almost mandatory.