Ok, so, let's see if I've got this right...
...having an OpenID login means I can use my Blogspot.com username (for instance) to log in to a completely different website (say, Amazon.com) and at the point of login I will be redirected to the Blogspot login page and asked to log in THERE as proof of who I say I am. If I give the right password into Blogspot, then I am redirected BACK to Amazon.com and am immediately logged in. It means I only ever have to interact with Blogspot - providing the website I want to log into actually ACCEPTS OpenID logins.
But I had to internet browse for 90 minutes looking at other youtube videos (including this very random but pure Mr Bean video) and web comments before I could feel qualified to make a decision about whether I would use OpenID, or not.
And I think I could find a use for it - maybe. I actually don't mind that each site I visit has a different username and password, kind of like a disguise I use depending on why I'm there (that's not as suss as it sounds!), but there are sites, like news and radio or basic fun sites for instance, where it doesn't matter if they know my Blogspot.com information or not. Ok, will give it a go.