Let's try and keep this focussed on Desire S users with problems, so that new visitors know what this thread is about, and how to fix them plus any updates to the situation..
Speaking of which, my Sensation is reporting an update to Android 2.3.4, which I'm downloading now. Cancel that - it finished downloading the 44MB in about three minutes and just as I started writing this sentence, so it's installing.
The fact that now, through this thread and others, I know we can safely downgrade our phones if we really must, I'm happy enough to try this without fear of no return.
Hopefully, the same kind of update will happen shortly for the Desire S and fix the problems that this thread existed for in the first place.
(And if it all goes t**s up, look out for a "Support Signal drops completely - HTC Sensation" thread soon!!!)