I have been using the TImex Global Trainer for approximately one month. This is a watch that provides watch features (Time, stopwatch, timer) as well as heart rate and pace.
Why use pace? For the past 13 years, I have been using heart rate as a training tool. The faster you are moving, the less reliable heart rate becomes. As you start to work harder, your heart rate will have a fairly linear increase up to the anaerobic threshold. After passing threshold, the increase in heart rate starts to level off. At any point along this plateau, the heart rate will remain relatively constant, despite increasing work. For high-intensity efforts, heart rate is not a reliable tool.
The second problem with heart rate is the rate of rise. If you start a hard interval now, it might take a minute and a half for your heart rate to catch up. This is fine for long, steady efforts, but short intervals need quicker feedback.
There are two reasons that I chose the Timex brand over the Garmin brand. First, I plan on using this for triathlons and the Timex offers waterproof ratings to 50m. Second, and this may be a moot point with the newer Garmins, I wanted real-time pace, not average pace over the last 1/4 mile.
Because my only other GPS device is my Motorola Droid X, this became my point of reference for testing.
Many other reviews have cited long times with GPS satellite lock. I also found this to be true initially, but then had no problems. To be fair, the last time I tried to use it, I started the satellite search while I was in the car, which is not recommended since there is no access to open sky.
As a pacing tool during my last 5k, it was spot-on for my pace and final time. Of couse, it actually works better as a pacing tool if you look at it.
When doing intervals, the real-time feedback is great--especially when running on level ground.
The other features, such as heart rate work as expected. The new ANT+ strap is a lot softer than the last generation of Polar coded straps with which I'm familiar.