I think bluetooth marketing can be and will be extrmely useful.  As the strategy to ue bluetooth grows more and more people will be aware of the ads sent to their phone.  A few things must happen at all times:

1: Bluetooth mesages should ALWAYS be an opt-in message.  Meaning that in the transmission request, we ask if the consumer would like to view the ad or promotion from company x.

2.  I do agree that there should be marketing materials to upport the usage of bluetooth marketing in the vicinity.  That accomplished two things.  First, its a call to action for the people interested in being marketed to.  Secondly, it lets consumers know to set their device to hidden or undiscoverable.  Not only will this detail increase the presence of your market but will also make the marketing strategy been seen in a positive light by warning the consumers who do not wish to be advertised to.

As far as bluetooth marketin being illegal, dream on.  it's very legal and in my opinion, the consmer has more control over what ad they wll view than the TV, intenet and radio.  Consumers can reject the request to view that ad and never be sent that ad again.  I can't count how many times I change the telelvision channel because an innapropriate product is being marketed on tv while my kids are present i.e. viagra, cialis, herpes medcine, alcohol ads, controversial tv show commercials.  The list goes on.

Consumers who do not wish to receive thes ads or promtions just stay hidden and never worry about viewing that promotions again. 

Just for my own knowledge, can anyone give me an example of a time in which one would need their phone/pda set to dicoverable while walking through he mall, concert or ote venue?  I can't think of one.  Keep in mind that even in "hidden" mode you can still operate bluetooth linked devices such as headset, gps and others.