Partnership best practices?

When another forum other suggests forming a partnership, what form does that usually take for you? Revenue sharing mods/posting on each other's site, each taking on admin duties on the other's site, merging your forums, cross promotion?

 

I've never done this, but I'm assuming cross promotion is most common.

I wouldn't see a reason to share revenue, moderators post on the other forum, merging forums or even taking on administrative duties.

I'm sure someone who has had personal experience can give you a more eloquent response.