It's discontinued and now rests in well-earned obscurity as outdated tech. Though it is very sharp and rivals or is better than the 50/1.4, it has the horrible 80's-style af motor and is superseded by the ef-s 60 & ef 100 macros with longer working distance.
Possibly a hint that one of the new 50s maybe a macro that can command a premium price.
The 40 was a very intriguing product for me in that the build quality is up, IQ is excellent and the price a bargain. This last thing being the most puzzling as Canon have been exuberantly pushing up the price of their latest lenses. What that means for the new 50s is open to conjecture( as we have seen here).
The 50 1.8 has always been a bargain lens with great quality but build that falls short of other lenses in the lineup. A new 50 f2.0 with IS and stellar IQ, USM, IS and the build of the 40 would likely have a price in the neighborhood of $800 if the new wides are any guide.