Martin
This is a nice feature for admins/moderators!!
Just a few thoughts:
The main issue is it is not obvious you are in the process of moving a post. A secondary issue is that once you clicked 'Move', it is not obvious which post you are moving.
Most other actions on forum posts display the post message at the top of the page, then what you are doing beneath it (e.g. reply, forward); but moving doesn't do this.
The ideal (just my opinion) would be to have the context bar at the top, saying something like "Moving Forum Post from [Forum Name]", then display the post message, then the appropriate step in the process underneath that (i.e. 1st step - pick the target thread, or choose new thread, 2nd step - pick position).
I'm guessing the solution you have implemented involves fairly minimal changes, and I'm aware that my ideal requires new pages, or at least a restructuring with fragments (list of forum threads, post message, thread posts).
It may be possible to effectively turn existing pages into fragments, and have a single 'move' page collate the fragments and drive the process.
Just some ideas of the top of my head - not necessarily the best place to find them :)
<Raad>