I have the Ambit and love it! First off, it is expensive...actually downright crazy, expensive at $500 without the heart rate monitor. I won't even try to justify it's price. The fact is, if price is of concern, don't bother with the AMBIT. Truth is the ambit is the first watch GPS that is even worth considering for the backpacking/hiking crowd. Battery life is the standout feature of this watch. At 50 hours in GPS mode, it is outstanding. For hiking/backpacking, I don't use the watch in GPS tracking mode. I simply load waypoints of my planned trip (lakes, etc.) in the Suunto software through Google maps, and save those waypoints onto the watch. I also love being able to save campsites, trialheads and any other locations while on the trail. GPS location fixes are appox. 1 min. initially in a new area, then are ultra quick at a few seconds after that.
Once on the trail, I just use map/compass to orient until I want or need to see how close I am to a particular waypoint. I'll turn on the GPS function and see how far I am or what direction I need to be headed. Again, most of the time I don't need it but it's nice to have a backup if the trail or area is unkown. The GPS function is only used intermittent and sporadically. Hit the back button and your back into watch mode- not using battery in GPS mode. Being able to quickly check your current location coordinates and verify that on my printed TOPO maps (with UTM grids already printed on them) is fast and accurate. It has limitations like all technology, but it is far improved in tracking/reception and lock-on time, over my older Garmin Etrex Vista. Time will tell. Also, having the altimeter is great for backing up your location on a map without having to go into GPS mode. Overall, I am very impressed. Being able to have all the practical GPS functions in a small, light, watch is incredible. Having the ability to have longer battery life vs. other GPS watches is the differentiating selling point of the Suunto.
Some will complain is doesn't have routes or doesn't have enough battery life for longer tracking but, I never used a GPS like that anyway. I use it to verify and assist in traditional orienteering. With this in mind, it works great for me and would others as well. Sorry for the long post. I'll have a detailed review on my website soon.