Wells Fargo and a couple others allow anywhere from 8-16 as their maximum, though I reduced mine to 12 because some ATM's were kind of finicky at the longer lengths.
Luckily (hah) working for a US company so I don't get enough time off to actually go overseas, so it's never been something I had to worry about.
Edit: It doesn't seem so weird anymore either. I used to get questions all the time from Cashiers, like "Wow, I didn't know your PIN could be longer than 4". But I haven't been asked about it in 1-2 years.