Merge two forums?

[SoundSystem]

Hey,
I've got a vbulletin 3.7 on my .co.uk domain and a 3.7.4 on my .com.
I want to merge the .co.uk into the .com, I'm pretty sure I use impex, but I want to know how easy it is?
Will anything from my current forum be removed? How is the overall process.
Cheers

[Dismounted]

vBulletin -> vBulletin is pretty much flawless AFAIK. If there are two users with the same username, there are two outcomes:
1) If both emails are the same, merge accounts.
2) If they are different, add "imported_" prefix to the name.

Also, unique IDs will change.