I knew that upgrading my phone would spell some kind of trouble.
In this case, aside from losing a lot of settings (such as email accounts), my Bluetooth keyboard no longer works.
It's a funny problem, though. The keyboard still connects, and the driver works. You even get a sound when you press the keys. But Android 2.1 on the X10i doesn't allow you to select BlueInput as one of the input methods. It's just not there any more.
I tried installing the latest BlueInput, but no change. Wonderful.
[Edit]: To re-enable BlueInput in the IME list, go to Settings/Language & keyboard settings, and check "BlueInput". This will allow you to select BlueInput as an input method, and the keyboard will work again. Now using driver 1.7.
Note also that the stock Sony Ericsson backup application does a good job, but MyBackup Pro did a reasonable job of restoring my home screens. I'd recommend it.