The only real challenge so far has been, in sidewalk riding, being sensitive to the older folks (older than me!) of which there are many. The challenge is that, in the West San Fernando Valley, many older people here are Persian, Ukrainian, Russian, Filipino, Indonesian, Honduran, or Guatemalan and do not understand, "coming up on your left." A bell or horn scares them.
It's a great and wonderful thing to live among so many different cultures but it does have it's challenges.
Of course street riding in this place is tantamount to suicide.
It's an interesting dilemma. What are your thoughts?