My Dad turned me on to them a few years back, and it was a particular hit with my son, who's a huge dim sum fan, so we never would have made it out alive without at least paying a quick visit.
I've had a fair amount of dim sum, including places in SFO like Yank Sing, most of the well known places in Seattle and Portland, and even Hong Kong, and I've have to put Ton Kiang at the top of my personal list.
The individual dished are very well executed, and there is a ton of variety, including many dishes you don't see often. They have a whole series of shrimp dumpings, similar to har gau, but including different greens such as green onions, spinach, cabbage, and snow peas. It's well worth it to try them all. The dumplings are all quite small, which is nice because it means you can try more dishes instead of filling up on giant hum bao right off the bat. The fried taro was also exceptional. Not to everyone's taste, but one of my favorites.
Best of all, Ton Kiang is right down the street from the Wirth Brothers' Bakery, which is home to my wife's favorite poppyseed coffee cake in all the world.