I've had my Vista HCX for about 3 weeks now, here are a few of my observations.
I did a simple battery rundown test. I set the HCX to log a trackpoint every 10 seconds, I had WAAS on and logged to both the internal tracklog and external GPX file on a microSD card. I clicked on the backlighting a half dozen times. The HCX was sitting on a desk in my house and not moved. I was using CTA DB-24 (2400mAH) AA Ni-MH batteries. The result of this non scientific test was a battery life of 18 hours and 14 mins.
Along with the battery test, I was curious about WAAS vs Normal mode. I did a second test as above but with WAAS off and for about 14 hours. The results were plotted in Google Earth, the location was in Reno, NV USA,
Here's the trackpoints for WAAS off.
With WAAS on.
And Both together.
I do not know the exact location of the GPS in the house but there was less dispersion with WAAS than in Normal mode. The WAAS XY Variance = 2.79, the Normal XY Variance = 7.00644. The difference in the the two averaged location was about 1.6 meters. Another measure of dispersion is looking at the 95% ellipse area; For WAAS it was 52.4 meters^2 and for Normal it was 130.6 meters^2. So at least to me it looks like WAAS does help.
GPS Reciever Sensitivity:
This is subjective with no data to account for it. I used both my HCX and a 60 Cx from work. I had one in each hand as I walked in a moderately heavy, second growth, Eastern Sierra Nevada, Pine/Fir forest. Both GPSRs constantly held from 6 to 9 satellites, I consistently had WAAS corrections thoughout. This is in an area where a Etrex Legend C would only track 1 to 6 satellites, failing to hold a consistant fix and definately no WAAS. I can't say which was actually better, in my opinion they're pretty much equal. One other thing, reception appear to be pretty much equal for both GPSRs when held either horizontal or vertical.
Some other stuff:
I was marking fish capture locations with the HCX. I got a "Calender Full" message after 503 waypoints. The Vista HCX has a 1,000 waypoint max but evidently can only have about 500 calendar entries. I haven't tried but I assume I need to unselect the save to calendar in the Geocache Option to off to get more Waypoints.
There is definately a problem with the trip computer for walking. The HCX had half the distance as the 60 Cx. I'm sure this won't be a problem for biking and vehicles. The minimum speed for logging seems to be about 2.5 miles/hour. The new Compass Calibration nag screen is a pain but can be worked around until fixed.
All in all an excellent GPSR that will no doubt get better with future firmware upgrades.