I've been 25+ times in the US in the past few years, visited 10+ states. My shortest visit was only a few hours, the longest one more than two weeks.
One of the funniest (sometimes: most challenging) part of these trips is the immigration. You never know what questions you get or why. I've ended at the secondary inspection two times - this means you get a big red paper at the immigration and you have to go to a separate office where they can "inspect" you in more details. Sometimes it takes hours, but mostly because you have to wait.
The first time I got there was my second visit in the US. I was a kind of expecting this as I was 5 months pregnant with my daughter. They wanted to be sure I really leave the country BEFORE my baby gets born. I convinced them, was let in.
Second time was more unexpected. I was speaking at a conference in Toronto and wanted to visit a company is Boston. I had a flight booked early in the morning and back the same evening. When you enter the US from Canada, immigration inspection happens before you depart, still in Canada. I went to the airport early enough, but got sent to the secondary inspection. It turned out, I am suspicious because of several reasons: I had Hungarian passport, stayed in Toronto for a couple of days and wanted to enter the US only for a few hours. Moreover, I said I was speaker at a conference in Toronto! The officer got totally confused. He asked me to prove it. I had nothing printed out and they didn't allow me to turn on my laptop. I convinced them to open the conference's web site and check it for my name - but it was not enough. They wanted more, something "more official".
Then, driven by some crazy idea, I sent them to my blog as I had written a post about this conference in advance. To my biggest surprise: THIS was enough! They got impressed enough and let me run to the gate. I still don't know why my blog appeared to be more official than the conference site...
But besides this, usually I get funny questions at the immigration. Usually they ask the goal of my visit, sometimes they ask me about my job, but here are some "unexpected" examples:
Once I landed at JFK, the immigration officer asked me what I did two years before(!) in Seattle, WA.
Two weeks ago, when landed in Seattle, the officer's question was simply this: "Visiting Microsoft again?"
Now, coming to Orlando, landed in Atlanta. The offices checked my US address I provided on the customs form, and his only question was: "Visiting Mickey Mouse or Winnie the Pooh?" :-)
More to come...