OpenID lets you create an identity that spans multiple sites. There's absolutely nothing preventing you from creating multiple OpenIDs, so I don't see what your problem is with it.
What I really feel uncomfortable about is integration of identity systems into browsers, like "Log in to Chrome" or Mozilla BrowserID. Sooner or later, the only way to use multiple identities even across different websites might be to use multiple browsers, or at least a bunch of incognito windows.
I think your fears are a bit unfounded. While I haven't tried "Log into Chrome", BrowserID lets you choose which persona you want to use. Sure, this means you have to have a bunch set up, but somebody could definitely write a plugin to allow the automatic creation of throwaway BrowserIDs, akin to mailinator emails.
Also, Firefox lets you have as many browser profiles as you want -- I already use this to manage online identities, of which I have more than one, and segregating is useful.
Yes, it's definitely possible to do that. But switching between Firefox profiles is nowhere near as convenient as logging into two different sites with two different identities in two tabs next to each other, which is really easy to do if you don't share identities across sites. As I said, juggling multiple incognito windows is not fun. If anything, juggling multiple profiles is even less fun.
But I guess I'm just ranting here, since it is well known that convenience and privacy don't always go together.
"But switching between Firefox profiles is nowhere near as convenient..." - don't switch, run them in parallel. I use 6 different profiles and often have most of them open at the same time.
BrowserID allows you to select one of your multiple ids when logging in to each site. It's more of a replacement of the process of signing up with email/password to each site rather than an "identity".
