How important is it to have identical speaker cable length?

It is very important to have the same speaker cable length because the sound will change with different cable lengths but, you will only hear that on certain types of speakers.

The ONLY difference in wire lengths would be a very small amount of inductance capacitance.  Certainly nothing that would be audible.

At least arch2 is keeping it real. I would also be more inclined to have same length of cables for L/R speakers purely due to OCD. I would speculate though that coiling one cable vs other being straight has more chance of resulting in actual audible difference. 

Doesn’t matter but unless you are making your own cables, aren’t they usually packaged in matching pairs?

Truly great sounding systems come from fanatic attention to details. The little stuff adds up to be of major importance if you are working towards a truly great sounding system. You can get good sound out of a system made up of really good synergistic components. But for truly amazing sound you need carefully chosen cables, interconnects, power cords, cable lifters… tweaked room… etc. it is a question of what your end objective is. While you may not hear a difference outright in a difference in length, it will have a very small effect on the sound… it is a shortcut. Short cuts add up to a sub optimal. For me, instead of spending a couple hours trying to figure out if I can hear a difference, I’ll just go along with the recommendations from the professional reviewers and use equal lengths.