Strengths: I'm running my 3rd marathon in 12 months at this years' Flora London marathon, and I'm finding that with my Forerunner, I'm running the actual distances. In the past I've relied on little more than guess work, but now I know that what I thought was 18 miles is nearer 16, and my 6 mile run was nearer 5. This means that I feel much more confident that I'm running the correct mileage and I'm also much fitter for it.
Weaknesses: The buttons are a little fiddly and sometimes when you reach for the light you hit the lap button. I'd prefer the light to be on the front, like with the watch that I got free when i subscribed to runner's world. It's in a much handier place.
Overall: A great piece of kit that will motivate you to run further and longer. I love the virtual partner mode where you select a distance and time and the watch keeps you informed exactly how far ahead or behind you are. Ideal for those long runs where you drift off and find you've been slowing down.