The Change Parameters tool under Modify is great, and I use it while sketching to drive dimensions by simple equations that incorporate other dimensions. This short screencast is what introduced me to this powerful ability:
https://www.dropbox.com/s/y541asdj43l3imm/parameter%20sketch_carpentry_720.mov?dl=0
The only thing that would be nice, is when the Change Parameters window is open, clicking on a parameter under the Parameter column would cause the corresponding dimension to become highlighted in the sketch, so that I could easily identify the correct parameter to modify in the Change Parameters window. 