My parents have had five over the years, although Im not a big fan of the breed you may find it the best pet you've ever had.

None of my parents shelties ever had any health problems, their three that passed on died of old age.

Like kobieeli said they are VERY mouthy they bark at just about everything and they do require alot of grooming.

My parents shelties were and are not very social with other animals, but thats all in the way they were raised.

With love and training Im sure a sheltie would make a great pet, and yep they are amazing at agility.

I think there might be two or three sheltie owners on this board, maybe they will come help you out.