Guess I'm "in the process" of leaning toward primes, though I can't see ever getting rid of my zooms.
The Nifty Fifty hooked me. Now I've added an 85 1.8 that I really love for so many situations.
My daily walk-around bag is a Kata D-16 which always seems to hold my 40D, 580 EX II, a couple of homemade foam sheet velcro-ed snoots and bounce cards that store flat in the back pocket and are ready to modify light in an instant, the Nifty Fifty, 85 1.8 and Tamron 17-35 2.8. The Tamron is simply amazing and I really think of it as a prime in terms of IQ, with a bit of zoom flexibility. I rarely use my other zooms, but they're available if I need them.
Like most, I prefer natural light when I can make it work for what I want, but I use flash a lot, actually, on and off camera -- both subtly for fill and "natural" light effects and also more dramatically.
I might upgrade and add another prime or two someday, but I'm really pleased with the range and versatility -- and results I get -- with what's in my walk-around bag right now. (For more extensive shoots or longer travel, I can carry EVERYTHING in my Kata 3N1-22.)
I'm covered from 17mm-85mm, or 27mm-136mm field of view on my crop, for everything I do -- from street shooting to landscapes, low light, clubs, performers, action, indoor sports, groups, portraits, children, families, events -- all in one comfortable and compact holster.
Two of those three daily lenses are primes -- and the third works and feels like one. Frankly, given the IQ of the Tamron, I'm fine with its small zoom and versatility at the wide end (yes, it's a great portrait lens as well), rather than a prime.
But if I only had room or a budget for one lens, for what I shoot and the way I like to work it would be the 85 1.8. Hands down.