This subject comes up every so often. I've never regretted letting my hair go grey after dyeing it for years and years. Firstly, I discovered that my hair was not "grey" at all, rather a fab silver shot through with dark - and I liked it! Secondly no more sitting in the hairdresser's chair for hours, mentally drumming my fingers and finally, my hair is healthier again like it was before I started colouring it. I get compliments on my hair nearly every other day.
And - with my son's wedding less than a week away, I've just put a conditioning rinse through my hair called 'Powder' which has given it the most gorgeous fashionable sheen (it washes out and is just to enhance the colour for the wedding).