I didnt have a k1 pending back in october, but my third trip in a year
on the VWP did made the bells and whistles go off at the POE.
Be prepared for ALOT of questions, secondary inspection and an interview
in front of a videocamera. I didnt have an easy time when i came back in
through Philly as my POE. In the end i convinced them that i didnt have
any bad intentions and that i would be applying for a K1 visa once i
arrived with my fiancee and they let me in for another 3 months.
My suggestion is, as many have said, have PROOF that you will return. I
had a nicely written letter from my employer, cellphone contract (lasts
until end 2004), misc bills and proof of my apartment in Europe.
I was polite and answered every question truthfully (Are you planning to
work, how do you get the money to afford another 3 months, howmuch money
do you have on you, where are you working, etc).
I know that if the POE officer had a bad day that i would have been
turned back, So i am sure that you will have to go through the same
ordeal, since you have a petition pending that shows Intent to immigrate
(although its a non immigrant visa).