I'd been thinking about letting myself go gray for several years but never had the nerve to do it, mostly because of not wanting to look old at work. However, I had switched a gentler hair color a few years back that let some of the gray peek through between colorings, just to get myself ready. I used a color that was close enough to my natural color that I didn't even get serious "roots" with it, as I did with the heavy-duty level 3 permanent colors I used to use.
Last May, on our anniversary trip to Belize, I just decided then and there not to color any more. My hair was wildly curly from the humidity there, and I just decided I liked being natural and free. So, that's what I did. Haven't colored since.
My hair is a mixture of white, blonde, light brown, and very dark brown hairs, kind of a frosted look. I often think it looks blonde/frosted when I look at myself in the mirror, but when I see photos, it looks more gray. I can live with it, though. I used to have light ash brown hair when I was in high school/college, but after that I started coloring, so it's been interesting to see what it morphed into over the years. Here's what it looks like:

I feel very liberated!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow