Here's a list of average dates of last frost in Washington:
http://www.humeseeds.com/frost1.htm#WA

Early fall, September/October, seems to be the best time to plant potted plants. It gives them a chance to get established during the rainy season, so they need less supplemental watering during their first summer.

Early spring works well too. Early March? It is sometimes said that if the ground isn't too frozen to dig, then you can plant things in this region. I've lost plants that I planted in December or January, and not just in this year's big storm.

And now we'll let the experts answer. :)

Though the selection at nurseries is better in spring I've had far better results planting potted shrubs in fall. That first dry summer is a real killer. I lose something that I haven't resisted planting in spring every year.

Frost shouldn't bother any of those except gardenias. My Kleim's Hardy has survived several years but I would not say it thrives here. Mine is up against a cement porch for warmth.

I've planted gardenias twice and had them dwindle away. Apart from avoiding the coming hot weather and the cold, wet soils of spring the main advantage of planting hardy plants in fall is that there is a heavy growth of new roots during that season. Not much root activity occurs during winter, so if you don't get a particular item planted before it has its annual fall root rush you have missed the boat.

Fall root elongation occurs when the overwintering terminal buds have formed at the ends of the branches. Any tree or shrub that has stopped making new shoot growth and set buds may be in the process of stretching its roots or on the verge of doing so. With some specimens this could happen as early as August.

So should I just plant everything that I'm wanting in spring and water the heck out of it, or wait til hot August days to try to establish things. I'd really like to get the plants to survive, but I also want to get them growing so our neighbor's bedroom window cannot see into ours.

Bboy is right: the selection at nurseries is much better in the spring. Later in the year, plants are picked over and tired. If you go to a proper nursery, they will give you great advice about establishing the shrubs/perennials you purchase. Many times, they guarantee their survival. And, our rainy season often lasts until mid-July which gives the plants a couple of months of natural watering. Just make sure they don't dry out if the rain stops. I think April is the best time to plant -- it's unusual to have much frost after that. On the raised veggie beds, take a look at the GardenWEb "soil, mulch forum". They have some great ideas for lasagna gardening which is a little less work and gives great results. It sounds like you have a super project ahead of you. Enjoy!

It's also going to depend on what you are planting. Last frost dates really only apply to frost sensitive plants - like annuals or tender perennials. Hardy perennials, shrubs and trees can be planted at any time you can work the soil.

I've planted in midwinter, all through spring, sometimes in summer and a lot in fall. The success of these plantings has been pretty much uniform. This past December offered some rather atypical weather for most of us, so I would not use this season's late fall planting as a good index.

In this area, many nurseries and garden centers have fall planting specials where they bring in a lot of fresh, winter hardy plants and offer them at sale prices. Fall is really an ideal time for most permanent ornamental plantings but selection of very seasonal plants (spring blooming perennials or shrubs) is not always at its greatest at that time. I buy and plant whenever I find something I like or need - year round :-)

Something to consider is that if you rush to plant it in the spring rather than fall all you will gain is maybe 4-8" of new growth this year. Very little to do much for privacy. Best to work on establishing hardscape and amending soil and doing research. Stop at a local nursery or join a graden club for advice. Also, stumps can be beautiful! Consider keeping 1 or 2, especially if they're starting to decay. They're perfect for planting huckleberries, japanese maples and other plants on. If they get termites don't worry. Those are not the same species that damage houses.