For all those who are considering doing agility with their dogs, I strongly encourage you. Even if you aren't sure about ever competing, you should know that there are now so many different agility "venues" that there's really something for everyone.
If you have a very small Yorkie, the Teacup Dog Agility Association (the good "teacup" lol) is something to look into - the biggest inhibitors for small dogs are the jump heights, A-frame height and seesaw tipping weight but in TDAA these are,, and can be, all lowered.
A link to TDAA and many of the other agility organizations can be found here:
http://www.mightymitedoggear.com/linkstraining.html