Hmmm, 5%-30% click fraud? For someone spending, let's say, $5,000 a month in PPC that's just $250-$1,500 a month in fraudulent charges! Why worry, be happy ... and hope you bought Google stock at the IPO price.
I believe there are instances of specific advertisers being targetted by their competition, in which case the fradulant clicks could be far more than 5 or 10%. Even if click fraud is across-the-board at 30%, advertisers are still getting a way better deal then they would from the yellow pages or newspaper advertising. The people making the big deal about this are just click fraud protection companies and publicity hounds who like to see their name in the WSJ. I can only remember one case of Google going after a company for click fraud -- and that was over something like $50,000. Thats peanuts compared to the size of the PPC market.