While not a conclusive or scientific test by any means, I've found pretty good accuracy with my Vista. I have a survey certificate for my house which shows the elevation at the end of my driveway, and the Vista shows the same elevation there within 1/2 metre (I have it set metric and it only shows whole metres). On the beach it has shown 1-2 metres (at high tide, so I'm above the mean high tide level which is what elevation is usually based on, as far as I know). I've also checked it at a few mountain passes in the Rockies at known elevations (as well as a couple of airports, with published elevations), and it always seems accurate as long as you've had a decent degree of GPS accuracy since turning the unit on. That is, if you turn it on and get 22 metre accuracy, it may not be quite right until you wait for more sat reception to get better GPS accuracy so it can calibrate the barometric altimeter with data it's getting from the GPS altimeter. I have it set for auto calibration, as it seems to calibrate itself as well as I can manually by telling it the air pressure or a known elevation. That said, I haven't taken it through any major weather systems that might confuse its barometric altimeter; I'll have to try that some time while playing with GPS accuracy and see what happens!
Hope that helps!