When I sew two displacements, it doesn't seem to do anything, and I believe that I'm doing it correctly. I can still select the displacements separately. I feel like after they are sewn, they should be treated as one item? Thank in advance!

Sewing just merges displacement points together. Make sure both points are in the cursor radius though. It's good for cleaning up those tiny seams in between displacements.

AHHHHHHHHHHHHHHHHHHHHHHHHH I'm a moron. I just tried it, and it worked just as you said! I guess for some reason I thought "sewing" would actually sew the pieces together and make them one! But I guess this is good too :) Thanks man!

I finally figured out sewing the other day. I was doing things the wrong way for a long time.

Note that if two displacements do NOT sew together when you tell them to, it means that they are not aligned correctly. Zoom way in on the grid and check the corners.

The Sew button on the Displacement tab can be used to connect the edges of two or more selected displacement surfaces. You can sew displacement surfaces in any of the following circumstances:

Any two displacements whose base face brush surfaces share a common edge with coincident endpoints.
A displacement surface to a non-displacement brush face, if the base face of the two share a common edge with coincident endpoints.
A displacement surface to another displacement surface where a shared edge is exactly half the width of the other (called a T-junction).You can sew displacements with different resolution settings — the vertices of the higher resolution displacement will be moved to match the vertices of the lower resolution displacement.

lokky here; http://developer.valvesoftware.com/wiki/Displacements

When I first mapped, I had a hard time understanding that the displacement itself had no direct correlation to the geometry on the grid. So if you put two pieces of geometry in positions where their faces are not flush, even if you displace their edges to appear to be pretty much touching, they are not, and there's pretty much no way to make it look perfect. Once I understood it I fell in love with displacement. :cool:

Once I understood it I fell in love with displacements...
...and learned to hate the Vertex Tool

ya sewing displacements is easy and effective, two major improvments in this version of hammer. Making somethng like this would takes a long time with the vertex tool, plus youd prolly end up with invalid brushes and light leaks and all kinds of nightmarish things