I thought they were only going to replace the PCB for the power button assembly but when I got the phone back and started it up, it went through initialisation as if a new phone.

All my data was gone and the OS was back to Froyo (it was on GB when I sent it off). Yet it's the same phone body I think since the screen cover I had was still there.

I was able to recover most of my apps by just going to the Android Marketplace on the web and sending them down again and installing the rest from the SD card. But for some reason some I am sure I had downloaded were not noted as being downloaded before and I had to re-install them.

While I was doing that I got an OTA for GB so I installed that of course.

So it took me a while and I lost some data (data in applications that don't sync to the web) but mostly it's back to normal again. I supposed HTC actually replaced most of the inners of the phone including the internal RAM which would explain why it had gone back to Froyo since there was no other reason for them to do that to just replace a power button.