I use keyboard navigation a lot when composing mail and I frequently have a hard time telling when the address-entry control has focus. It would be nice if there were a better visual indication, like perhaps changing the background to a light yellow or something. Note, this problem is even worse on NS6, which sometimes doesn't even show a cursor, but I also have trouble on MozMail as well.
It's a standard among textfields to have the blinking caret indicate focus. Voting for WONTFIX. We don't want to special-case these textfields, because then we'll end up with an inconsistent UI. Also, this could be done by a skin author, if s/he wanted to.
blicking "|" is the known method