My Online Identity

I haven't yet read a good article that helps me understand my many different online identities.  Here's a quick list.

Facebook. I can login to a lot of sites with my Facebook credentials. I'm not sure if this means that my Facebook identity for others to see includes these places that I join? When I join and comment there with Facebook, does it show up on my Facebook wall?

Twitter.  There's very little that I understand about this.

Disqus - I've seen this around for awhile and never really understood it. I just clicked on one of my comments on a blog done through Disqus and found out that all my previous comments, done with the same email, are immediately available. Worse, I sound like a broken record usually making the same point, despite the topic. Embarrassing.

Google - I use to have a gmail account, a blogger account, and a Youtube account. They seem to have somehow merged. So far, they still seem separate from my Google Plus identity but I'm frankly, pretty confused by all of this. These accounts also have control of my Adsense, Adwords, and Analytics accounts.

Wordpress - Some of my wordpress accounts, not sure if they are the hosted or wordpress.com ones, seem to be useful as an identity when I want to comment on blogs.

Other identities such as digg and de.lic.ous and stumble upon and of course, AOL and yahoo, all seem to have disappeared.