I've been procrastinating for ages about how to handle forums on separate but related sites. They're all the same site concept, same fundamental topic (same design, branding etc, but split into three different mini-sites on separate domains for different continents, and even more ccTLD domains for different language versions of the content). The three main .com sites are linked together from the home page of each, and the ccTLDs are linked together multilingually on individual pages.
I've got one forum on the original .com. Running it is a total pain in the a### but it's very useful and generates a sizeable portion of the site's traffic. The static content country pages of the original .com site have a feed of the latest ten topics for each country, which is useful for leading visitors into the forum, and results in some sign ups.
I don't however like the idea of starting from scratch with a new forum for each minisite. As I said, even though the site is spread over domains. it's all the same website concept. Would I be running any risks by just keeping the same forum, scaling it up with new sub-forums for the other minisites, and then running the last ten topic feeds into those domains from the original domain.
Sounds confusing, but I'm sure you get what I mean.
Note: All WHOIS is transparent. a few of the sites are on my server in Singapore, a few of them are on my server n the UK, so they have a few IPs... but everything is transparent.