As I've been trying to transition from heel-striking to what is arguably the more natural midfoot-striking position, I've been increasingly using lower profile shoes like the Brooks Pure Flow and Saucony Kinvara for more of my general running. I've used Kinvara versions 1 and 2 for shorter to medium length runs but tended to think they were a bit light for me on some of my longer training runs.
The Kinvara 3 has won various Best Update awards and I can see why. The new, FlexFilm upper makes for a better fit across the top of the shoe. I found them slightly roomier and more forgiving in the toebox on longer runs, which suited me. The outsole has been bevelled to give a smoother transition and has more XT-900 rubber for greater durability. They're still super-light for a training shoe at only 218gm but I've found that they're lasting really well.
I'm sure it's partly because my running style has finally changed a bit, but I'm now using the Kinvara 3 for nearly all my training. I'm as happy running a 20-miler or more in them as I am doing a shorter tempo run. The triangular lug pattern on the outsole even means they're even good off-road unless it's really muddy.
I've had a few favourite training shoes over the years but I can't think of any that I've enjoyed running in as much as the Kinvara 3 and that is praise indeed!