Glad to see your site, Rob, as no-nails playing deserves better press than it usually gets. I play both with nails and without. Not hard to do, since I use nails held on by adhesive dots, heh. I spend a few hours each week playing without nails, which I enjoy immensely. It's a different feel, and a different sound, certainly.
For me, one of the greatest factors in playing without nails is environmental noise. Now, I'm not talking about a jackhammer or boombox nearby, but things like a refrigerator in the next room, or traffic noise a half mile away... background sounds one doesn't usually notice after becoming accustomed to them. I find that when I'm playing without nails, I need something much closer to absolute environmental silence (as if that's actually possible) than when I'm playing with nails.
"I got a fever. And the only prescription is more cowbell." Christopher Walken