I see the convenience, but that only works if you're willing to bare your soul to Google. If you want to have one identity for YouTube, a different identity for Gmail, and don't want Google to know where you are via Maps, that becomes much more problematic.

I wouldn't quite say I've "bared my soul to Google". I slowly signed up for those services as they became available and now I only have to login to one of them to use them all. If I don't want Google to know about me for something I just open an incognito tab.

If you have multiple google accounts like the gmail website in a browser on a PC, you can switch between them by just choosing the account from the google accounts menu. Tremendously convenient. Google can have my figurative "soul" for this.

Comparatively if I have to switch between my twitter accounts, it's way more convoluted than it needs to be on a PC/browser. Still, it used to be much much worse when going to their login page gave you a redirect to their app download page. It used to take me ages to locate a workaround.

Sounds like a good opportunity for a browser that manages your various identities across multiple sites.

Chrome has had this feature for years. You can create separate Profiles for YouTube, Gmail, etc. I do this with Facebook to minimize exposure to the Like Button virus.

How do you access this feature?

The 'People' section in Settings. There's also a button with your profile name on it at the top right in newer versions of Chrome.

Is there any way to stop this automatically picking up who I am when I log into GMail in the browser? I don't want Chromium picking up my identity just because I logged in once.

Same, except for Youtube.