Order of preview/submit buttons differs for forums and wiki editting pages.
When I am starting new discussion on forums I have two buttons on the lefthand side: Preview Post and Submit Post.
When I am writing a reply to some discussion on forums I have two buttons on the, conversely, righthand side: Preview and Post reply.
When I am editting a Wiki page I have three buttons on the, again, lefthand side: Cancel (not highlighted with green background), Submit and Preview.
For the first two cases, buttons' labels differ slightly and Post reply does not follow Book title naming convention, but the most confusing is the change in the order of submit and preview semantics of buttons on Wiki. I'd suggest making these things to be in order, because it seems to me that they may serve as a source of unpleasant submits when preview is wanted.