Here's what I do, now, to type those people I know fairly well.. I take the following test as though I were them: http://similarminds.com/cgi-bin/newembj.pl
I'd normally just think through the letter combos and deduce a type for the person, but when I've known them long enough, I've seen to much variation to be objective. This "embodiment" strategy is working really well for me now!
I also had a couple people take the test as though they were me, to see what their perception of me is, and each one saw me as an ISTJ!!!! Something to think about..
I also did this to determine the type of my "ideal" personality.. it came out ENFJ. Interesting.