I remember reading this article by a guy who wants to discourage the use of booth babes. Here's one of the suggestions that appealed to me:
The Tactics: Actually, this part is pretty simple. When the first person at a booth approaches you, treat him or her exactly the same way you would a sales or implementation engineer. Ask questions regarding the technology. Ask about planned life cycles of the software, on use counts, and other things. Treat them exactly as you would an equal.
If this person is a booth babe (or a clueless marketing droid), they will inevitably hand you off to the lead technical (or sales) person at the booth. Here comes the important part: Demand to know why they wasted your time with manning the booth with clueless people. Don't discuss sales or tech with this person (which is what they will desperately want to do at this point). Ask why their company wastes everyone's time and their investors' money using people who provide no value. Tell them that you will not be doing business with them, regardless of their technology, because you believe that any company that needs to hide behind tricks, gimmicks, and sex appeal, can not offer you any value. Point out that a great number of their competitors don't need to use flimflam to sell their wares. Then walk away.