So what is it

Here's the technical bit AMS
And the numpty version.... An account manager is a web site that facilitates finding and joining BOINC projects.
An AMS is a neat web based page that you can sign up to to control all your computers, this is only for signing up to projects and changing global settings. It doesn't do anything like BOINCview as that is not the point of an AMS.
You simply hook BOINC up to the AMS through the Attach to Account Manager option, enter the URL & Password and its all connected
I have been using one for a long time now and it makes signing up to a project so easy, I simply log into my AMS page, go to a projects page and if there is a new one I want to sign up to I just press the attach button, and hey presto when BOINC connects to the AMS it is issued a command to created an account at that projects, attach me, set the global preferences and download new work.
You can also detach from projects this way and re-attach existing accounts.
BOINC connects to the AMS regularly to ensure it is using the latest settings you have, it can also be forced to connect to the AMS if you don't want to wait for the next automatic connection.
There are currently 2 out there and both are in BETA Testing, one is with a Branded BOINC Client, and the other is a Independent one.
As soon as the one I'm using is ready for more people I will post the link to it, so that anyone interested can use it.