weeks - 3:44 pm on Mar 9, 2011 (gmt 0)
I'm struggling with this myself. But, from a practical point of view, I need something that can help me with management of content across all of the social platforms.
Also, I think your list leaves out email, with is a basic.
One friend of mine is using Fliptop (which sounds like what you are looking for), but I'm just using MailChimp as a base. They are working hard to make it work with social. I feed the emails to the client's website, FB and Twitter, then using Twitter to intergrate with Linkedin. I think this will come close to providing what you need on items 1,2,and 4. But, then, I'm keen on email.
Re: #3--Anyone offering "brand perception/influence metrics" is blowing smoke, of course. There is a service called Trackur that follows keywords, but you've got to follow the right keywords. And then it's just keywords.