Is it good practice to length match all traces of DDR3, or are only data traces important?
Generally speaking, there are two sets of signals that connect to a DDR3 memory:


Address and  control signals, which flow from the memory controller to the memory chip(s), accompanied by a reference clock.
Data signals, which flow in both directions between the controller and the memory, accompanied by a separate strobe signal.


The trace lengths within each of these groups should be matched, but the matching between the two groups is not as critical.