Firstly, oops! The absence of a link was a mistake. I have added a link to the first mention.
As for multiple sites … on one hand multiple presences linking to each other can help people find you in one place or another either through improved rankings or just because you are everywhere. On the other hand setting up a dozen sites with all the same content distracts people from any one site so my suggestion is to have a primary site and if you have a presence on other services, link them to your primary site and perhaps include a feed from the primary site into the satellite services.
My sense is it is better to focus attention on your main site to build up traffic on that site and awareness of the site itself. Satellite sites can help with certain things and they could spread the brand but they will distract attention away from your main site if loads of people link to one of them. On the other hand, if you handle the content right, they could become a great channel for new visitors.
Anyone else have any thoughts on this?