In short: no.
(Thanks for checking up on this; I’m glad that you the other member that sent me a private msg on this matter are actually taking the time to read these–or at least my–posts this well.
)
While there are many CMSes that technically have this capability, I have yet to find one that integrates with a forum (namely phpBB) without having to modify said forum software/database significantly…or simply be a proprietary forum flavor. To be clear: I want to build a phpBB forum set and decide at any time to “link” forum topics with CMS articles (in each direction) at any time, while still being able to operate both the CMS and the forum independently (save for the article-and-forum-topic cross-links) if need be (say I like one CMS flavor one day and a different one then next…of different ones for different sites/applications/topics).
There are some that come close, namely Mambo’s phpBB forum integration. However, Mambo still requires a ton of MODs to a phpBB database/software set such that said phpBB forum can no longer accept a lot of the other, non-Mambo MODs that I require (and I’m not sure the resulting phpBB forum can still live on its own, either…but if any of them can, I’d like at Mambo’s setup first).
There seems to be a big fascination with single-user-signon in the CMS-to-forum development-integration world. While this is helpful, in most of my smaller communities (which tend to be development-related), I suspect it’s not such a big deal. In any case, I have yet to find any significant CMS or forum application that does not have some sort of LDAP tie-in for which I can probably solve the single-signon problem anyway. My point being: CMS-to-forum integrators seem to be so obsessed with single-signon features and miss the point I’m trying to solve, and that is link content with discussions (in essence, structured content with unstructured content).
One of my key forum-MOD objectives is to run every one of my forums with seamless email-list “synchronization,” as per what http://mail2forum.com/ (aka M2F) provides. However, M2F 1.0 currently requires native phpBB software set, and not a heavily-modified one (like Mambo’s or many of the other phpBB derivatives/copycats for CMSes). An aside: I really do not understand how forum admins and email-list admins can live with so many communities that suffer because email lists do not have forum-archive capability and forums do not have email-interaction capability. I find myself truly stunned by this deficiency in the state-of-the-art in open-source software. This capability is a staple of even things like yahoogroups.com, but yet when I went to the vBulletin folks and begged for them to insert this functionality, they dismissed me rather quickly (and imho, rather rudely–I tried to press on and then I think I aggravated them in the process, so I gave up).
But back to my main point: I still have not found what I’m looking for.
I’m hoping that phpBB 2.2, and its supposed API development, can allow for better and cleaner MODification (for both CMSes and for things like M2F) so that module/add-on integration can be much easier and less interdependent.
Having said all that…it’s been about 6-8 months since I tried to scope most of this out…and I also may not have been privy to all the best info then, either…so if anyone wants to dispute and/or add on to any of the information/assertions above, I invite them to contribute to this topic-thread. I am always interested in learning more. 
-Matt
ps: I want to do the same thing (linking discussions with content objects/articles in an “independent,” modular fashion) in the context of Wiki’s (and the Wiki entries) as well. In fact, I think there are so many powerful applications of linking discussions (or other, non-structured content/data/info) with some sort of structured content that (like CMS articles or Wiki entries–that hopefully establish some sort of structure over time, or at least have the capability to achieve structure)…or even linking any content with a discussion…that I think a general model/API for linking content with discussions should really evolve from the primitive organisms that we are using now so that we can basically link any discussion (be it “instantiated” in the form of an email, web forum, newsgroup, etc) with any content object (be it a book, CMS article, Wiki entry, etc). I would think this would be quite powerful. Heck, just the ability to link the discussions together across multiple “interfaces” (web forum, newsgroup, email, etc) would be extremely powerful in and of itself.
Sure, many can argue that their software already does this. But does it allow one to pick and choose which software they use for each module? Can I choose any forum software to go with any mailing list software to go with any CMS to go with any Wiki…and then tie it all into the same site/system with few integration headaches? I highly doubt it. Right now, a site admin is forced to get all those things together only with proprietary integrations; they (the site admin) can not choose each application to serve each different purpose. If they could, they could then possibly choose what they think would be the “best of breed” for that purpose (be it email list, CMS, Wiki, web forum, etc) and not have to be saddled with the limitations of the “proprietarily-integrated” modules/application.
Maybe one day we will be able to make this choice. Until then, we seem to be pretty far away from this capability.