Have imported bikes both into Japan and from Japan to the U.S. Throwing a bike into a box and sending it off is easy, the devil is in the details. Do you speak Japanese? If so, you can save some money by clearing the bike through customs yourself, renting trucks, driving around Tokyo (!) etc. Also, where will the bikes be stored once they get there (space costs money), etc. If you're dealing with a shop owner or other middleman, that can also work out differently than you expect it to..... Every biker is a buddy over a beer, but when there's money and Harleys involved, well, you know how it goes.
If you're dealing with a middleman, it might be best to have him pay you cash for the bikes, then send them off and let him deal with everything on that side. Either that or do everything yourself on both ends. As with everything, people are the biggest problem. "We'll sell them in Japan for a huge profit and then split the money!" Yeah, right.
None of my deals went sour, but for the amount of hassle involved it wasn't worth the time and effort. Still, with the yen at 77 to the U.S. dollar, the potential to make some money is definitely there.