(This is actually old news in a sense -- the new $5 bills came out in Nov. with changes to prevent this kind of "reuse". However, there are still counterfeit bills out there.)
I overheard a local businessman today say that he got stuck with three $100's which were printed on bleached $5 bills. You can identify them by holding them up to the light and looking for the watermarked portrait (which is imprinted into the paper and cannot be removed by bleaching) -- if the printed and watermarked portraits don't show the same person, it's counterfeit.
It's been ages since I've even seen a $100 (that's why I'm a Democrat) but I would sure inspect one carefully before accepting it.
http://wclo.com/news/2008/jan/17/counterfeiters-hit-beloit-businesses/http://www.wsbt.com/news/local/10947821.htmlhttp://www.csmonitor.com/2007/0920/p14s02-wmgn.htmlhttp://www.treas.gov/offices/domestic-finance/acd/if-you-suspect.shtmlhttp://www.treas.gov/usss/money_detect.shtmlEDIT to correct Pogo-like spelling