I am planning on hosting on behalf of my Japanese clients and wonder if by doing so I would be slowing down their websites with extra links. There are good connections in Japan but as prices are higher I am considering hosting in the U.S.

Theoretically you'll see a slight slowdown in the speeds between hosting in Japan and hosting in America. That said, there are enough backbone links to America from Japan (as far as I can tell anyway) which should ensure you shouldn't notice *too* much difference.

You could potentially see very little slow down or none at all. I recommend tracerouting any host you might go with from as many location in japan as you have access too. You might want to try tracert.com or traceroute.org, or some other public traceroute page. However, you need to remember that a trace from a bad connection will only yield bad results.