One apps for domain account is tied to my job, another my personal domain, a third to a former job/personal domain that I registered services with. I used my gmail account to access services that google doesn't make available on google apps for domains.
It seems that no matter which google service I'm using, I'm logged into the wrong account. I frequently can't log out from the other account properly on the login page so I have to go back to a mail interface. It is an utter mess. I don't care about google connecting the dots and realizing that I'm the same person in all the places. They make it so frustratingly hard to use and depend on their services that I'm actively looking for alternatives.
Linkedin handles it fine, when someone tries to friend me on my professional email address with linkedin, they know that I'm the same person. Google+ doesn't. I don't have a Google+ account on my preferred email account because I can't figure out how to enable it for that domain. I get Google+ friend requests regularly on every email address I have.