All the foregoing having been said, and conditions permitting, I share lanes.
It's one of the few benefits of riding a motorcycle in a cage-eat-cage world.
Sometimes I'll do it for a distance then claim a space in a full lane for myself. Sometimes traffic just seems 'angry'...it's during these times I opt out of the lane-sharing scenario.
Interesting, also, is at least here in SoCal, some freeways have wider lanes than others. For example, through sections of OC and LA, the 405 has VERY narrow lanes; and conversely, the 805 here in SD, south of the 8 has very generous lanes.
Another practice we engage here is called 'threading traffic'; during which the motorcyclist advances to the limit line at a traffic light or stop sign. I don't know what the rules are in other states on this particular activity, but it's a huge time-saver and generally (if you're an experienced, stable rider), very safe...as traffic on both sides of you has come to a complete stop.
One thing is absolute. While "sharing," one can never EVER take a break from an enhanced or heightened level of caution.