There's been a lot of buzz the last week of so about the case of Rescuecomm vs. Google over the around the not-so-simple question of whether bidding on trademark keywords is considered a use in commerce, thus violating trademark law.
As a Google program manager in the past I've seen both sides of this particular conundrum. When managing a Google Adwords program I've used both trademark keywords and misspellings of them that were my clients and those of their competitors'. I've also been on the side of companies running affiliate marketing campaigns where I monitored publishers to be sure they weren't using the trademark keywords in violation of their publisher agreements.
Part of me sees this as a free market economy...users are searching for products and services and everyone wants to get their attention and whatever words will get them there is what it takes.