John, there are many threads about this in the MYOG forum. It might take some digging to find them, but they have a lot of good information.
In my opinion, bonding with a liquid adhesive (Loctite Hysol U09FL and U09LV, or one of several contact adhesives) gives the strongest seams in cuben. Sewing and taping are used by cottage manufacturers and some in the MYOG crowd because they are quicker and less laborious. Many tarps with sewn and/or taped seams perform beautifully, however, and prove to be durable.