Regarding sewing vs. bonding, I favor bonding but sewing can work well too if it's done right. There's a big anti-sewing cuben movement going on right now, but I don't think it's as simple as that. When you sew cuben, you just need to be sewing enough layers that the stitches aren't going to stretch larger holes in the material. So if you're just overlapping two pieces of cuben and sewing them together then you'll likely run into this problem. Just one or two layers of cuben isn't strong enough to prevent sewing holes from enlarging and perhaps ultimately tearing out. Even if the seem doesn't totally fail, it looks poor and it's hard to seam seal if the holes keep growing.
What you could do if you wanted to sew two panels of cuben together is to fold the edges of the panels first so the material is double thickness at the edge and then overlap that, so you are sewing through a total of 4 layers of cuben. 4 layers of cuben is awfully strong and the stitch holes shouldn't enlarge under reasonable use. This may not be the most ideal way of connecting these panels but it should be a solid way of doing it that won't fail you. In general, I would say that sewing 2 layers of 0.7oz cuben is too little (for something highly stressed), 3 is borderline and 4+ is going to be fine. Even sewing two layers is fine if it's not a high stress application. I have some cuben stuff sacks that are sewn with just 2 layers and they are doing great.
There are some situations where sewing may be preferred over bonding. The only example I can think of is when a join is unavoidably going to be stressed in 'peel' rather than 'shear'. Even the best bonds make me a little nervous if they are designed in peel, whereas I would feel fairly comfortable with the same join sewed, provided there is enough layers of cuben so the holes won't stretch. An example of this is the top of a stuff sack where the cord runs through. If you fold the top of the stuff sack down (like rolling up your pants), leave a gap and then bond it to create a channel for the cord, then this bond is going to be stressed in peel a little bit because of the thickness of the cord. I've probably lost you here because this is confusing stuff to explain.
Here's another way to look at it. In the picture below, the tie out points are designed largely in shear, but there is a bit of peel forces going on because of the black plastic bar than runs through the loop of cuben. Since the bar is a few millimeters thick, it wants to peel open the loop of cuben. In this case the peel forces are pretty minor, but there are still some at work. If I was to sew a few stitches along the edge of the fly right where the cuben loop exits, then I would eliminate any chance of this join peeling open. I have actually done this and sewed a small box at each tie out. I didn't do this because I didn't trust the strength, but because I couldn't think of a good reason not to. In this case I'm sewing through 8 layers of cuben, so any stitches are going to be very strong and not stretch larger holes.