This kind of feature is in a few cad programs when in sketch mode, ala NX and Solidworks. It's more of a time saver when laying out a sketch to a rough shape you want, but then you have to go back and 'constrain' the sketch by adding dimensions to the lines and arcs, you can't give an accurate dimension on the fly.

[EDIT] Correction. you can type in an accurate dimension on the fly but then slows you down when you have to stop at each arc and type, I always find it quicker to do my arcs later.

~Danny~