Version: 2.70 test release (win 64)
I apologize if this is already known, but it appears that this feature is not implemented in the 2.70 test builds that were released yesterday. When transforming an object by entering a value, the header display does look different, but does not accept any math operators or letters. To reproduce, try transforming an object in the 3d view by entering a simple math expression (2*6, 100+73, etc.).
Did this feature simply not make it into this particular build, or am I using it incorrectly? Again, I apologize if this is the case.