We gave a presentation on writing PostGIS spatial queries at OSCon 2009 last week. Slides will be available on the site, but you can download them here as well.

Some of the sample data were were using you can grab here

PostGIS 1.4 is finally out as well, and hopefully should be hitting your favorite distros soon if it hasn't already. For windows users, we have compiled binaries http://postgis.refractions.net/download/windows/ for 8.2,8.3, and 8.4 and hope to have the stack builder installs sometime next week.