I'm thinking of getting a custom bike w/ S&S couplers as well.

It looks like a bunch of reputable frame makers are now including it in their service. Check out this website: http://www.sandsmachine.com/

There is a comment from Greg Lemond and Richard Sachs in their if you browse through enough.

My problem is which bike to get for this (sigh). Steel or Ti---but that's another subject altogether.

The savings you make from avoiding airline surcharges will make up for the cost of the couplers in about 3 or 4 roundtrips.