Shane, You may want to look at using 3M spray adhesive. This makes a very strong and water tight bond. Bonding is on contact so take care in having seams lined up correctly to begin with, practice on some scraps first.
David, With the spinnaker and cuban fabrics now available some may say use silnylon only if under extreme price constraints. If only it, silnylon, had less stretch and did not wet out...! Having said that, I feel silnylon offers a great performance to cost ratio that is hard to beat (hey that sounds kind of like tyvek).
With the amount of interest shown on this site in Henry Shires new tyvek Sublite I think the fabric has merit and is a viable alternative for MYOG projects. But that's just me.
IMHO all fabrics/materials, like hikers, have unique qualities that can be considered either strengths or weaknesses, how to best manage each is the trick.