The latest edition of Wired carries a story on the uptake of ID theft with a simple demonstration for how you can do that - as soon as you have e.g. someones social security number. That reminded me of a good suggestion from Jon Udell, which is to do an occasional Google search for your social security number. It is supposed to come up negative - if it doesn't you could be in serious trouble. Obviously your number may still be out there but a partial test is better than no test at all.
The same search strategy should apply to other vital statistics, your credit card number etc.

Sensitive information like this raises the only real issue with archives like the Wayback Machine, since automated complete archives would heighten the risk of exposure: If your sensitive data was published by accident at any time in the past the perfect archive would still have a copy of it.