A new command has been added to the Fillet drop-down in AutoCAD LT 2012.
BLEND is related to FILLET and CHAMFER, but it creates smooth splines between objects instead of lines or arcs.
Before and after:
The shape of the spline is almost entirely determined by the position and angle of the two objects it’s connecting.
You do have a choice of continuity, though: Tangent, which creates “a degree 3 spline with tangency (G1) continuity”; and Smooth, which creates “a degree 5 spline with curvature (G3) continuity”. The method you choose will affect the shape of the spline at least slightly, so unless you know in advance which one you need you can try both to see which one you like better.