The 2d DCA is modifying its formatting guidelines to change the spacing recommendation from at least 1.2 spacing to at least 1.5 spacing. So this means if you're using the recommended 13-point font size, line spacing should be set to a minimum of 13 x 1.5 = 19.5 -- so Exactly 19.5 complies -- but heck, just round up to Exactly 20.
When this was mentioned at last night's LACBA Appellate Courts Section meeting, Justice Grimes emphasized that this actually really is important, and PJ Rothschild chimed in (delightfully sarcastically) to say that the formatting guidelines really don't matter at all--unless you want your brief to actually be read!
There were many fun zingers last night, including Judge Ikuta characterizing the short and often opaque Ninth Circuit memorandum dispositions as haiku-decisions.