Now, with the terrain brush, you can move the verticies around laterally (sp?) to make it looks much smoother.
Also, you have the freedom to chose any grid size. Here, it's still 128x128 segments, but I used a grid size of 16 to edit the terrain.
Note how much smoother it looks. It is a lot higher poly, but now you can make much better looking terrain, you can use a segment size of around twice as big as you would with terraed and it would still look good. Here, if this was a portion of a much larger terrain brush then i'd be using segment size of 256x256 which would give 4 times lower polys than what is shown here.
(normally I'd have segment size of 256 or 512 and use a 64 grid setting to edit it. 32 in some places if it's an emergency.)