I like the way that Twitter is able to bring like-minded people with complementary skills together quite naturally and through self-selection. One of my favourite (reported) overheard descriptions of Twitter is:
It’s like IRC meets the whole world
In this largely text-based world live many writers, songwriters, musicians, and alongside them, many businesses concerned with all three. @ravenousraven is collating songwriting tips, and @ianshepherd is dispensing music production and mastering advice.