I don't recall if I've used the Facebook app today on my Pre, but when I tried to sign in after finishing my FrankenPre2, I got a 401_UNAUTHORIZED error. The description says: When in development mode, only application owners can use this method. Surely that has nothing to do with developer mode being enabled on my phone. When I tried to log in via the accounts app, it said invalid credentials. I don't know if this is related to your error or not, but it has me wondering. I also checked my apps on the website and the webOS apps are all missing, and if you search, they don't come up. Going to try again on my Pre here in a minute.
Developer of: SMS Auto Forward/Reply, GPS Viewer,
Keyring converters for CSV, eWallet, & CodeWallet
Touchpad Patches: Keyring HD, ClassicNote HD, YouTube HD (for 2.1 app)