If you're going to use Sketch Bones, the 'smoothness' has a lot to do with where you place your points. I get nice bends when the points are aligned with each joint. You also want an equal number of points on either side. Bone Strength can also affect how smoothly the limb bends--the more they overlap, the smoother it gets. Up to a point anyways--go too far and you get mush.
Also, don't trust the OpenGL preview. Moho will sometimes simplify curves for better interactivity and performance. You need to render it to see the
actual smoothness quality.
There are other ways to do 'bendy' limbs. Victor came up with an excellent technique using only two major bones. There are some limitations with the technique (you won't use this for 's' wiggles, it's more for 'c' bends,) but it can work really well for some characters.
BTW, using another technique by Victor, you can have both types of limbs in a character, and switch between them as needed. At my workplace, I've done this for several characters and it works great!
Victor's bendy limb tutorial is here:
viewtopic.php?f=9&t=20410&hilit=rubber+hose
His sub-rig switching technique is described here:
viewtopic.php?f=9&t=30445&hilit=rig+switch