I was with a client yesterday, sharing the idea of a community concept on the blogosphere, and we were discussing pros and cons about a marketer's participation in a 'community' concept, over limiting the presence to just a blog 'owned' by the marketer.
There are, in my opinion, a couple of compelling reasons, favouring the community logic:
The first, is the simple concept of 'you scratch my back, I will scratch yours' - media is becoming prohibitively expensive and as against spending precious dollars promoting just your property, marketers stand to gain from a collaborative effort - everyone benefits, more.
Second, the community usually sees bigger participation of/from users, than what an individual brand may be able to garner, as it caters to many different needs, tastes etc.
Third, analytics - this is the decisive reason in my opinion - consider this...
I write about FM/ Radio quite often on my blog and at this moment 8 of the 9 FM stations, except Fever 104 (and that got mentioned just now, so all 9) feature on my blog. Given that I sometimes feature high on FM related searches, many of these queries land on my blog.
Now using simple tools, I can tell you which one among these is the most searched radio channel; where are these searches originating from and much more. This is valuable information for a marketer. Possible because ALL stations are mentioned on my blog. The same rule applies to a community blog - you can learn much more about your competitors, by being in a community. Simple!