Recommends doing code review by email so you get a change log, even if people are in town (unless you are doing a sprint).

Recommends ~200 lines of code, 400 max. White space doesn't count, comments do.

All code for major projects at Google is reviewed prior to check in.

Tools:
http://codereview.appspot.com/
http://code.google.com/p/rietveld
http://review-board.org/

Slides