I have never purchased a GPS watch before so have nothing to compare this with. Other reviews seem to say it is an improvement over older models, however I can only speak from my experience of this.
Firstly, I had problems installing the USB stick driver onto my PC. Having contacted Garmin support they suggested I turn off or uninstall all my security software (anitvirus / firewall etc.) and try to reinstall. I shut down as many programs and services as I could, after first disconnecting my PC from the internet, and tried again, but to no avail. Eventually I found the answer on a forum after searching on google, and it seems many people are experiencing the same problem. In the end I had to start the installation as usual, until my computer hung. Then reboot windows into safe mode, to complete the installation, then reboot back into normal mode and start the ANT program running.
After successful installation it began to upload runs to my PC without any problem. However, in the last week, the software has now started to error when it first attempts to upload a run. When I restart the software it appears to upload the run successfully, but doesn't always work successfully, meaning I have lost some of my runs.
As far as the GPS goes, this is not perfect either. Last week I ran near my home, but by the time I had walked (a couple of minutes) to where I was going to start, the watch had not found the satellites, so I started running anyway. Three-quarters of a mile later the watch had found the satellites. I'd been running in an open park area, and there were no trees or buildings that should have blocked the signal. Also, when viewing runs on the computer after having uploaded them, there are sometimes small gaps where it looks like the watch has lost the GPS signal, and sometimes the recorded route seems to differ wildly for short distances from where I've actually run. In addition to this the inclines and declines recorded seem to be way out in places (though I'm not sure if it gets this information from the maps, or GPS). Unfortunately, all this makes me question how accurate the distances are it is telling me that I've run.
Having said all that, the GPS receiver seems to work better when I've run in areas outside my hometown, so perhaps I'm just unlucky with where I live!
I do still like the idea of the device, and what it tries to do, and in spite of the above, I think most of the time it is fairly accurate with the information it's telling me. I'm planning on running my first marathon this year after starting running 5 years ago, and being able to review the runs I've done, and use the watch to help pace myself over the miles has been really useful. However, for the price that I paid for this item, I would expect it to work near perfectly, all of the time, and for me it's too glitchy. Therefore I can only give it 3 stars.
UPDATE August 2011: Having used watch for well over a year now, I would like to update my rating from 3 stars to 4 stars. I think my initial problems with installation and getting used to using the device lowered my initial opinion. Although still not perfect (from the perspective of picking up satellites quickly - although as pointed out by others it is fine if you wait until you have them before starting), I have discovered and used many more of the useful training features, and found this overall to be an excellent training aid. I also use it for cycling now, and the feature that allows you to upload and follow your route removes all the hassle from navigating in areas you are unfamiliar with.