Spline IK Experimental Features:

1) "Even Divisions" - This option ignores the length of bones when considering how they should fit along the curve. This is useful for getting a smoother curve fit without having to worry about getting the bone lengths spot on. By default, this is disabled.

2) "Keep Max Length" - This option prevents the bone chain from extending past its natural length when the spline is stretched beyond that length. When the spline length is substatially shorter though, this bones get scaled to zero; making this option possibly useful for doing "growing tips". 
This is essentially a 'no scale' option, although the behaviour when the curve is shorter is really a compromise since the curve cannot be accurately satisfied + left intact without some scaling being applied due to the way this works.

3) "Radius to Thickness" - The average radius of the spline between at the head+tail of each bone determines the x+z scaling of the bone.

release/scripts/ui/properties_object_constraint.py

@@ -36,7 +36,7 @@ class ConstraintButtonsPanel(bpy.types.Panel):
 
             # show/key buttons here are most likely obsolete now, with
             # keyframing functionality being part of every button
-            if con.type not in ('RIGID_BODY_JOINT', 'NULL'):
+            if con.type not in ('RIGID_BODY_JOINT', 'SPLINE_IK', 'NULL'):
                 box.itemR(con, "influence")
 
     def space_template(self, layout, con, target=True, owner=True):
@@ -597,10 +597,17 @@ class ConstraintButtonsPanel(bpy.types.Panel):
 
     def SPLINE_IK(self, context, layout, con):
         self.target_template(layout, con)
-
-        row = layout.row()
-        row.itemR(con, "chain_length")
-        # TODO: add the various options this constraint has...
+        
+        col = layout.column()
+        col.itemL(text="Spline Fitting:")
+        col.itemR(con, "chain_length")
+        col.itemR(con, "even_divisions")
+        #col.itemR(con, "affect_root") # XXX: this is not that useful yet
+        
+        col = layout.column()
+        col.itemL(text="Chain Scaling:")
+        col.itemR(con, "keep_max_length")
+        col.itemR(con, "radius_to_thickness")
 
 
 class OBJECT_PT_constraints(ConstraintButtonsPanel):