If an employer tries to contact you via SO careers you get a "click here to view your message" link. If you click it and aren't logged in, you have to log in.
This brings me to two issues I had:
After logging in, you don't go back to that message you were trying to view. You just go to a generic home page thing.
There is no indication that I have an unread message from an employer. No red number at the top. Not even some kind of "Messages" or "Inbox" link. I've clicked around a bit and I still honestly have no idea how I'm supposed to view that message aside from clicking the link in the email.
Edit: So I found it-- you have to go under "My Profile" then there is a "Messages" link. I'd suggest that this is a bad place for the messages. Usually the "Profile" link on a website is for the purposes of editing one's profile.