My Penny is up to 15 lbs now! I love her size-- my fiance and I really like hiking and stuff, and it is great to have a dog who can keep up for miles and miles, and is large enough that we don't need to worry about her becoming too cold when we are at high altitudes and run into snow.
I picked the biggest pup in her litter of rescued babies, and I'm very glad I did-- one of her brothers, who was far smaller, wound up having a shunt. He thankfully improved after surgery to correct it, but it was still sad and stressful for the family that adopted him.