I think we can all agree that this site is slowly becoming a great WordPress resource and I find it much more rewarding answering questions here than on the WordPress.org Support Forums.
Some thoughts on getting the word out:
Reach out to some popular WordPress blogs and ask them to take a look at the site and write about it.
Someone from MikeSchinkel Enterprises could write a really nice guest blog post highlighting some of the questions and answers.
Have a WordPress Plugin contest using the StackExchange API
Build a Twitter Bot that updates every time a new question is asked
How can we get a piece of the StackOverflow WordPress tag?
The WordPress tag on SO gets an average of 13 or 14 questions a day which is about the same as our average. Most of those questions would fit here.
How are we doing compared to the other SE Beta Sites?
In terms of users we rank 18th out of the 22 StackExchange Beta Sites. At least we are doing better than Bicycles and Home Improvement.
What other ideas does everyone else have to promote the site and increase users?