I've been to St. Mark's Veterinary Hospital twice - both for sick pet rats. I really, really appreciated the fact that they were as respectful to me as they were to people who came in with more traditional pets like cats and dogs. The desk staff and all of the vets and assistants that I spoke to were very nice, calm and knowledgeable, and, most importantly, gave a sense of understanding that when your pet's sick it can seem like the end of the world. I was also impressed that the vet helped me understand what was wrong - like showing me how she could tell that my rat was dehydrated.
I was particularly impressed when I had to take one of my rats in to be put to sleep. The Dr. explained what was going to happen and, even though it was already early evening, gave me as much time as I needed to say goodbye. The experience hit me harder than I expected, and the vet and the receptionist were both so concerned at how much I was crying that they checked to make sure that I had somewhere to go and someone to be with afterward.