[masraum]

I've crossed it 4 times. You can miss an entire day if you think about "I took off from Cali, Seattle, etc... on Day X, and I landed in Japan, Vietnam, China, etc... on day X+2." If you hit the IDL at 23:59:59, then yes, you'd essentially miss a whole day.

One year we left the west coast of the US (can't remember if it was Cali, WA, or AK that we flew out of that time) on Jan 3 and landed in Japan on Jan 5. My parents' anniversary was Jan 4, so they missed it. BUT, the pilot announced that it was midnight on Jan 4, and then 2-3 hours later, announced that we passed the IDL, so we changed to Jan 5. So my parents had a very short anniv while in the air.

Non-stop from San Fran to Tokyo is ~11 hours.

When we (family) crossed the IDL, we flew from Tampa, Florida to a small military base in northern Japan. I think most of our trips involved 3-6 stops en route. I was a kid so I don't remember all of the stops. We made the trip from FL to Japan twice and Japan to FL twice. I know we usually took off out of Tampa or maybe Orlando. I know that I've landed in St Louis, San Fran, Oakland (I think), Anchorage, Honolulu, Denver, Chicago, Atlanta and I think Tokyo. I think we might have also hit Atlanta, Dallas, and maybe Phoenix. Then we'd take a bus to a military base near Tokyo and catch a hop in the back of a military plane (C-130, I believe) from there to our final destination.

The military booked us on cheap flights that the airlines couldn't fill up, so they weren't concerned with how long the trip took or how many stops we had to make.