If you really want a fast 50, then the f/1.4 wins the day. It's a better lens than the L in virtually every respect for a small fraction of the price.
I'm thinking about moving up from my 50 1.8... Kind of stuck between the 1.4 now, or waiting a bit (not necessarily a bad thing, since I do have the 1.8 if I need it) and saving up for the 50L or seeing what sigma releases for a new fast 50, since their 35 has been such a big hit. I'm curious why you say the 1.4 is better than the L in virtually every respect... I know about the slightly curved focal plane the L has, but does the 1.4 do other things optically better? or is it just the smaller/cheaper/lighter that you're getting at?
The 1.4 is sharper at every aperture from f/1.4 on, especially in the corners (due to that curved focal plane).
Really, all you get with the L is an extra fraction of a stop of maximum aperture (with a depth of field so insanely narrow that it can only be considered a special effect) and "better build quality" that doesn't include weather sealing.
The 1.4 is a superlative lens. The L isn't a better lens; it's just a slightly poorer performing, heavier lens that opens up a marginal fraction wider. And it's got some red paint. And it costs three times as much That's all.
I wouldn't call the L a bad lens; indeed, it's almost as superlative a lens as the 1.4.
however, describe the L as far and away the absolute worst bang-for-the-buck in Canon's lineup.
If your reaction to learning that you'll be out-of-pocket $1500 for repairs on your car is annoyance with the hassle of dealing with the rental while your car is in the shop, then the L is for you. Otherwise, if you'll actually notice $1500 missing from your bank account, the L is the last lens you should buy.
Another 50 worth considering is the f/2.5 compact macro. It's the sharpest 50 Canon makes, one of the sharpest lenses you can get period, and has essentially no distortion or other flaws. Autofocus kinda sucks, but if that and the merely-moderate maximum aperture don't faze you, it's otherwise probably the best 50 on the market today as far as optics goes.