At my FLGS, 40k is the dominant GW game to play. Not saying there isn't a healthy amount of fantasy players (because, there are), but the amount of 40k players to Fantasy is about 3 to 1.
As it has been said, I have begun to notice that the fantasy players at the shop tend to lean more towards the older crowd. I used to be very large into Fantasy when I was younger(I'm 20 now), but that was mainly due to all the really cool models; and not to mention, the feel of controlling a literal 'army'. (not just a 20 man skirmish force of space marines!)
As of right now, I'm strongly considering building a Lizardmen army, (admittedly due to the amazing new models, and feel the army gives off) as well as playing 40k on a regular basis. So I'm not going to be one sided on which games I play. Another FLGS that I have been going to just reached module 1 on the GW supplier chain, and has thusly begun to move into the realm of tabletop games. 40k is the dominant game there as well(if you count 6 or so people as dominant), however, one of the guys that work there and I have been trying to push people into trying Fantasy as well so as to raise popularity.
In the end, both games are awesome. They each have their own quirks, and styles of play, but we play our games because they're fun to us; not because they're popular.
1750 pts of painted Ferro Zoican Chaos guard
1750 pts painted HH World Eaters
1500-1750 pts of soon to be Raven Guard
1250-1500 pts Rust-crons