I just purchased a Motorola Defy XT from Republic Wireless and it came with the Facebook app pre-installed. I immediately checked for a system update (which there was one waiting), installed it and the FB app went away. Usually it doesn't work out that nicely though. My last Android was the HTC EVO and you couldn't get rid of FB unless you rooted it your phone.

The Google Nexus One had Facebook force-installed; (I think) it came with one of the OS upgrades, which is even worse than pre-installed, because I really had no choice.

It certainly was one of them on some phones. I have had a "Facebook for LG" in the past that wasn't removable via the factory phone image.

Nope. The Samsung SGH-T959V (T-Mobile Galaxy G 4G) came with it preinstalled. I had to root the device to get rid of it (among other things).