I would’ve listed this particular pitfall higher up on the list, probably behind Not Getting 401K Match, since it’s similar to that pitfall; but this one involves not taking advantage of the various IRAs that may be available to you. Roth IRAs allow you to do some tax-free investing and other IRAs allow you do some tax-deferred investing, either way your principal grows without the burden of tax.
One other considering is that there may come a point when you can’t take advantage of an IRA, the 2007 income phaseouts for the Roth IRA starts at 95k and ends at $110k (single filers).
Source: Yahoo Finance