The BBcode for Centering seems to only work on one line. So you can center one line of text but for instance if you have a large block of text and you try to center the entire post it doesn't seem to work e.g

[center] 

vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv

[/center]