I friend of mine just received his brand new Vista HCx - and it shows version 2.70 (for both, software and GPS). So far he didn't experience the inaccuracy problem - so there is hope!
Unfortunately that version is not yet available for download, but maybe Garmin wants to give it a slow start to avoid a similar disaster as with 2.60...
My own unit notoriously and persistently kicks me off the track after extended caching walks. First I believed it was related to WAAS/EGNOS, but switching that feature off didn't help.
The worst experience I had was the position being off about 200 meters after a walk through a woody valley in the shadow of a steep hill.
I think it's acceptable that position isn't that accurate under such conditions. What really makes it bad is that the unit doesn't recover from this situation, even if left alone under perfect reception conditions for a while...
I developed the habit to power cycle the unit multiple times when approaching a cache location, just in case...