Crosschaining is really only an issue for big-big or small-small combos. Pretty much anything in-between will be fine in the course of a normal ride. WRT the "double shift", I think I understand what your saying, and yes, I occasionally will simultaneously downshift from big ring to small while upshifting one cog....this generally happens when I'm nearing the big-big threshold and want to maintain cadence while jumping into an easier gear without getting into a big-big combo. I don't know that I understand about "shifting twice or even three times [sounds like bologna for an 8 spd cassette] in the opposite direction" as you mention, except to note that Shimano STIs (and I think Campy and SRAM too) allow you do downshift multiple cogs in a single motion (for Shimano, it's up to 3 cogs).