If you have a heavier dog, or 2 or 3 yorkies, the pet strollers really are great. They are excellent for taking the babies to dog-friendly outdoor events. You don't have to worry about them walking safely through the crowd and you don't have to watch like a hawk for larger dogs. If I don't want people to know there is a dog inside I just throw a baby blanket over the screened front, and the dogs can still see out the back. I have this one and I think the quality is great.
http://www.pawshop.com/hatrpetst.html