I have been working for american companies remotely for a while, I do fairly regular visits to the american offices, generally 'Work Meeting' will get you straight passed, but I have a few times been questioned exactly what I do at these work meetings and once tiredly and mistakenly mentioning programming, was very close to being refused entry.
The other issue I couldnt find any documentation on how long a visa waiver is valid for, it is given for 3 months, but is that 3 months out of the year or just 3 months at a time? over a full year I occasionally get close to this and was mostly curious.