I've read conflicting info around the webs regarding this exact question. Posted and didn't get any bites, so I decided to donate my phone and a few hours to the cause. To make a long story slightly shorter:
I had a rooted stock 2.2 phone with S-off Cwm 5.0.2.0.
I downloaded the stock recovery from dougpiston.com and flashed it.
Rebooted the phone with stock recovery, noting I still had S-off.
I applied the OTA file someone captured from their phone and uploaded to xda.
Rebooted. Success! Running 2.3.4 with the new kernel, radio, etc.
Flashed Cwm 3.0.0.8 from dougpiston.com
Revolted into Cwm and applied the su-efgh file from dougpiston.com and got back root.
The HTC calendar had to be frozen (with ti backup) because it kept my phone awake after the update, but I didn't clean caches or do a wipe or anything before applying it. I suspect if I had, or do a wipe now and reinstall, that problem might disappear.
As many said, the build.prop is screwed because it reports a 4.3 inch screen. I saw a patch on xda I'm going to apply.
The phone IS faster, scoring better on linpack as well as feeling snappier in use. Haven't used it enough to determine battery life changes.
Anyway, if you absolutely cannot wait, I can attest it will work, if you reflash that stock recovery to apply the update, and that you can get root back if you're S-off before the update sink its teeth into your phone.
Probably old news at this point, but hope it helps someone.