1. Create your motionPath as you normally would
2. Select the "motionPath1" node in you Channel Box inputs and you should see "U Value" and it should be keyframed. Select that attribute and Break Connections to kill the animation. This "U Value" is just like "Parameter" in PointOnCurveInfo nodes in that it will move your connected object along your curve using values 0-1. You think it would be that simple but you will likely get Cycle Check errors.
3. To clean up the setup and avoid errors you can use the connection editor to connect motionPath1 (allCoordinates "xyz") to the translate "xyz" values of whatever object you have attached to your path, and then simply delete the 3 addDoubleLinear nodes that are no longer necessary.
This leaves you with your curve->motionPath->attachedObject and also gives you all the other options that are built into the motionPath node like Follow, Twist, etc. I usually attach locators to motionPaths rather than directly attach objects and also like to use setRange nodes to expand the 0-1 value of "U value" to something more friendly to interact with like 0-10 or 0-100
source - Andrew Hake
