We spent the better part of a summer cruising the south sound and Hood Canal shooting video for our WA State Marine Parks Cruising Guides (Volume 2). It is quite a departure from the more familiar and desirable cruising grounds in the islands and beyond, but we thoroughly enjoyed our time down there. For one thing it was like being on a lake most of the time. And all the larger boats we encountered were heading north.
We always recommend visiting Hope Island State Park (the southern one, not the one up by Deception Pass). Only an hour out of Olympia, it has some historical features (and old farmhouse) and a very nice, long walk around the island. Very peaceful, yet so close to the state capitol.
The other thing we recommend for south sound cruising is belonging to a yacht club. The reciprocal opportunities are very good from Seattle south. Because we were "working", it was nice to be able to grab a slip every third day or so and have computers running all day to get caught up.