Not a very interesting question in and of itself, but I'd like to get some numbers to use in a following question.
If what you're really looking for is something like the relative popularity of 50mm f/1.4 vs 50mm f/1.8 lenses, you might look at membership in Flickr groups. For example, I added up the number of members in all the groups whose names started with EF 50mm f/1.4 and the same for EF 50mm f/1.8. The totals were 22008 and 21172, respectively. This doesn't really tell you anything about sales figures, but you could infer that among people who enjoy sharing photos on Flickr, the two lenses are roughly equal in popularity.
Another measure is Amazon's best seller rank for digital camera lenses. As of this writing:
items #1, #3, #4, #27, and #33 on the list are Canon, Nikon, or Pentax 50mm f/1.8 lenses
items #6 and #26 are Canon and Nikon 50mm f/1.4
item #40 is the Canon 50mm f/1.2L
From this, one might infer that more 50mm f/1.8 lenses are sold, at least through Amazon, compared to f/1.4 versions.
Of course, you hardly need Amazon to tell you that when two products do nearly the same thing the one that costs 2-3x more than the other will likely sell in lower volume.