There is a slight seem on the side but I don't think it is too noticable. Its a damn shame there is no "extrude" function, that would make it so much easier. The inside part was frustrating because since it was so small, it would only have one division, so I ended up just making a simple brush and filling in the spot.
so I gave it a shot and it worked like a charm for the outside curve. The issue I'm having is with the inside curve. It seems it only bends in the middle, while it should be bending 3 times:
If i move the center vert to the right and down it becomes straight:
Make sure the vertex points for the side patch lines up the vertex points of the top patch looking from top-down and that they are properly snapped to the grid.
If you still have the problem, it could be because of a bug in GtkRadiant 1.5.0. Sometimes patches don't weld the seams properly. It works properly in 1.4.0. Even if this is the case, it should still compile fine though and Q3Map2 will merge the seams as it should.