I gotta ask you (granted I have been a rather aggressive advocate for the PS4, constantly arguing for it lol) have you really researched it? Have you sat down with the flurry of informatoin on IGN and really weighed everything out? I assume that touch pad will simply be for web browsing, and the cross play with the Vita, as most games on the Vita have silly touch oriented controls. Now be aware that it is a pad, not a screen, which one makes it less funtional, and less expensive- next, I will say I am dissapointed in there being no BC, but, most gamers aren't overly... nostalgic. I won't honestly miss my PS3 games. They aren't the benchmarks of my gaming experiences- now I do miss my PSP because that was my first hardcore gaming handheld.
That being said- you really need to read all the articles IGN has put out on it. All of them are simply informative, not opinion based. And that share button is equated to the start button, as well as its main function is to simply record your play sessoin.