what's linking where?

OK, I think part of my frustration is that when I'm working on my mac at home, it automatically links some things to others based on which gmail I have open (or maybe it's just capricious...)
I have a Google account with a Yahoo address, a personal gmail, and a work gmail - and the work gmail doesn't support all of the apps. So I get utterly confused trying to figure out why Blogger gives me messages like "You are not an author on any blogs" - from my own blog - or why when I click on something in Google Reader it changes the options in other windows I have open. I'm trying to decide if I should try to figure it out (again) or just go with the current approach - blinders, and the same password for everything.