Spontaneously, I'd yell "I like this feature too!". Until I start to ponder a bit deeper.
Here's the catch: please keep in mind that people may wish to use different accounts for different sites.
For example: someone might want to use their professional public self on the main programming site, but use a private alias on the "for fun" code golf site. Similarly, it is also likely that there are several real persons using the same computer, not necessarily with their own private OS login which would have helped separating web browser cookies.
- I have my public main account registered to various sites on my work computer.
- At home, I also use the same account on a couple of those sites. As well as a private account registered various other sites for private "hobby stuff".
- When checking one of the sites on the main account from home, I might get a cross-site notification about a post from another site, where I'm not logged in at from the home computer.
- Then when I attempt to login at that site, the dumb thing instead finds my private account in some cookie jar and tries to log in with that one. Effectively blocking me from logging in with my main account to that site on that computer.
- If I log out the private account, I can no longer log in to the sites it was previously logged in at, because then it finds the main account instead. Catch 22 deadlock.
Please, no automatic cross-site logins based on cookies. Or at least give people the option to log in and log out at each site manually.