[fleitz]

I feel bad for the guy, but having been across the US border a few times it's important that if you're travelling for anything but spending money in the US you'd better phone and find out if you need a work visa.

  Volunteering? VISA.
  Working for free? VISA.
  Might ask someone for change? VISA.
  Speaking at a conference? VISA.
  Having coffee with someone and may discuss business? VISA.
  Friend might buy you a beer? VISA. 
  You plan on bringing your bags to your hotel room yourself? VISA.

Exceptions: If you are going straight to your hotel, then going to disneyland, going back to your hotel and back to the airport then you might not need a VISA, as long as you also know the flight number, airport, airline and seat number you'll be leaving the US on, then you might not need a VISA but should probably phone the consulate and find out anyway.

[RWeaver]

I bet the tourism companies inside the USA are over the moon with where this is going.

[MichaelGG]

First, it's visa, not VISA (which is the credit card company).

Secondly, your examples are not correct. You're allowed to come over on visa waiver for business (it's one of the options to select), just not to perform work for compensation. You can certainly attend meetings.