A splendid uS timescale PID loop is to be found in the following research paper. Email me if you do not have access to this journal - I'll mail it over to you.
"Teaching physics with 670nm diode lasers - experiments with Fabry-perot cavities"
R.A.Boyd et. al.,
American journal of physics 64 (9), September 1996. Page 1109.
Don't let the rather eclectic title put you off - it's a fab paper.