A really extensive list of brands utilizing twitter can be found at this location, called the twitter brand index. A lot more, than I thought, and a lot more US-focused (for obvious reasons) than I would have liked.
This at least solves the question: is twitter already relevant for marketing? It does not yet solve the question: is it effective for marketing? But that question will probably only be answered much later, once the user base of twitter has reached a critical mass.
As micro-blogging expands beyond Twitter, and communities develop across the Internet, I think it’s very important that brands maintain presences on places like Identi.ca, too.
It’s smart to listen to and interact with your community; it’s not smart to rely on one single tool or service to form those relationships.
True, it’s not about tools. However none of the other tools seem to have established a substantial user base – yet. Once identi.ca has enough users, brands should consider that, too.
Hmm… I would actually argue that the earlier you’re listening, the better a position you’re in. Depending on your brand, this may not matter, but I’d rather be on there to catch the *first* mention of my company (or relationed conversations) than to finally sign up and discover I missed four opportunities.
It probably really depends on your brand. Listening is important, no matter what. Engaging in the conversations on every single platform out there might simply not be feasible – both in terms of ressources, as well as return on investment…