(disclaimer: skip to the bottom for my point)
the first bit of advice I ever got before I even purchased my first DSLR was to ditch the kit lens and buy prime lenses. I was all for it for a while. I got the 50mm 1.4 and eventually the 35mm 1.4L (which I use for my video work). BTW I'm on a 60D. Just before I purchased the 35L, I thought, "man, this is really gonna upgrade my photos". In a way, it did. Colors are awesome with this lens, control over DOF in video and stills is awesome, and on a crop, I feel it's a great all around focal length for my photography. I had the expectation that having an aperture this large would solve all my low light problems but unfortunately it didn't. I still feel the strain on my 60D and it's high ISO noise limits. This forced me to look at my technique and eventually learn more/better ways to use my flash(es) (onboard, 430ex ii, and 600ex-rt). When flashes are used well, I can get pictures to look more like the way I see them in my head but the metering in my camera is now useless. My shadows are more interesting and I feel like I can create "moods" with my pictures using bounce flash and some OCF tricks. If I'm using a flash, I don't need as wide of an aperture that primes offer so I went back to my 24-105L. Maybe this will all change again when I upgrade to a full frame camera.
My point: my primes don't completely solve my low light woes (at least on my 60D) but they offer very narrow DOF if I need it. For portraits, they are great but I still like using primes with a couple flashes. I'd rather walk around with the flexibility of my 24-105 zoom and a flash or two.