It's really hard to generalize about temperament. They have a reputation for being reserved but not all of them are.
Toyo is 2 and he's pretty active, he barks at people he doesn't know, and wants to run up to every dog we see on a walk and goes apes**t when I don't let him. He's also not a lap dog but occasionally hangs out on the couch with me. He also spends a lot of time in his "nest". I put a bed under my corner bass trap behind the couch. That's where he sleeps and hangs out a lot of the time.
My friend's Shiba, Kochi, is pretty outgoing with people but has dog aggression issues. She and Toyo get along, though.
As far as health issues, they can have knee and hip problems but we haven't seen that. Kochi suffers from allergies and that appears to be part of her line. Too has an allergy issue from late August until fall due to the high pollen, probably ragweed. His legs and feet get itchy and he chews them. I keep him on Prednisone for the duration and that keeps things under control. On his last checkup, Toyo showed some signs of juvenile cataracts. That probably won't be a real issue for years and it's correctible now.
Google+ has a community for Shiba Owners and Enthusiasts. It's mostly a lot of Shiba pictures but there is some discussion about their personalities.
Jim
