I love my Forerunner 301 but damn I look goofy when I wear it for events or just running in general. It does a great job tracking my heart rate and has a decent application to display the routes I took. It is a great tool for motionbased.com if you are into boasting your achievements (not that I am into that or anything). I use my 301 mostly when I hit the trails on my bike, which sadly is not that often. It has a great virtual trainer that forces me to push myself when I am fading which helps a lot when you are alone out there.
The Forerunner 405 took what worked from the previous models and put it in a practical package that, though not very stylish, at least can pass as an ordinary watch. What is interesting is that it can sync the data collected from my training or events and upload them through a wireless connection to my computer OR to another 405 lover. I wonder if I can use the heart rate sensor from my 301, but first I need to find a lot of green stuff as this one will be a strain on the wallet ($318). Take a look at the vid to see the watch in action.