I also keep a spreadsheet with returns for all my holdings. The last column is a weighted average of return that reflects my AA. From there I use STDEV for each holding and my portfolio. What's even more valuable to me is tracking correlation of all my holdings and my portfolio overall (discussed a few months ago, available thru search).
No one agrees with other people's opinions; they merely agree with their own opinions -- expressed by somebody else. Sydney Tremayne
Retired Jun 2011 at age 57
Target AA: 50% equity funds / 40% bonds / 10% cash
Target WR: Approx 2.5% Approx 20% SI (secure income, SS only)