If it's occurring on the original Desire as well as the HD, it's not a 2.3.3 issue. Nor is it a network issue as it's happening on various networks. I'm guessing it's app related.
What apps have installed/updated over the last few days?
It's def either an app or some sort of problem with time itself. I have noticed a couple of strange vortexes kicking about outside over the past couple of days.