It's funny that you should mention using Williamette in combination with other hops.
I recently did an experiment using 4 different hops in 4 different one gallon batches. The grain bill was the same in all four beers and the amount of the hops was adjusted to reach a similar IBU level in each. The idea was to see for myself if there is any real difference in flavor with a single :60 min bittering addition and, if so, which flavors do I prefer.
After fermentation, I tasted each sample and did notice "subtle" differences. Some hops had more "flavor" than others. I found that Williamette, as a bittering hop, is pretty neutral. The interesting thing is that when I tried blending some of the finished beers, I found that the Willamette blended very well with two other hops from the test.
My favorite combination was Williamette and Simcoe. I think I'm going to formulate an American pale ale with these two hops and see how it turns out.