Here's some additional perspectives:
- The Web is drowning with content, photos, videos and text. Search is breaking under its weight and that drove the rise of Discovery. Discovery, via tags or categories, provides a level of organization that straddles chaos and the hyper-organization which is Search (of course, being gamed via SEO)
- Such organization is best accomplished in a casual way, where it's near painless for people to post to, or view their streams, in a multimedia way
- In this paradigm, vertical market players should have an advantage over horizontal platforms, only if they want to concentrate on content quality (and they should want to change this as the content is the ultimate driver of viewers....especially repeat visitors). Quality begets quality, having schlock devalues the brand.
- At its heart, many sites are vertical market custom publishing systems which become content platforms that address specific markets. Today, much of the content is community curated. This will be complemented via algorithms which understand what is of interest to whom (e.g. personalization via behavior and the social graph).
- The 'free lunch' of ripping off content from artists will eventually come to an end. Tumblr, Pinterest, et al, will have to reach an accommodation with copyright holders (often independent photographers or videographers).