First off, they are generally a one person dog. They will get along with others in the family but prefer one person over the rest.
They don't take well to strangers. They have a tendency towards hypoglycimia since they have very little body fat from which to draw energy.
They make GREAT doorbells when someone comes up in the yard or knocks on your door hehe.
Adult Chis don't usually intergrate well with children unless they were brought up with them.
They are highly intelligent and comical at times. Most of mine will pick up food and either munch on it in a seperate location or try to bury it in the middle of the floor, and then be surprised you can still see it when they get done burying it.
One thing to look for when shopping for Chis is weak stiffles or knees. Hold the prospective pup in your hand on its back. If the back legs cross they stand a chance of having knee problems later in life.
Having a Chi is like having a 2 year old all the time. They are always into something and picking up various little "tidbits" off the floor and carpret just like a youngun.
Another thing to be wary of is an open fontenael. Most all Chi pups have one but the smaller the better. I have one that is 3 years old and he still has a open font. Most will close within the first year but its still something to look for.

Chi's normal lifespan is around 16 to 20 years. Currently my oldest is 13 but I got him very late in life as a rescue. Poor guy was horribly abused before he came to me.

You just can't beat a Chis loyalty though, in my book.