Though I loathe the Twitter->LJ with a hatred that burns like a thousand suns, I think Twitter->FB isn't as bad. As I don't tweet I have no opinion on LJ->Twitter or FB->Twitter but the latter seems like it should be fine. As for LJ->FB I think it could work if you don't have a huge overlap in your audiences on the two (which I don't) and don't mind everyone on FB reading everything you wrote on LJ (which I very much do), so I think it could work for some but not for me.