THE HIDEAWAY 2219 Fourth Ave, 441-0464 It's only been around about a month, but already the Hideaway has made its mark on Seattle. The new venue, located where Sit & Spin used to be, held an impromptu after-hours show with the Bronx and Lot 6 when those bands recently swung through town, and it hosted a show with Electric Blanket and Popular Shapes where both groups took the stage at the same time, alternating songs. The cozy bar opens up into a large, loud showroom, and they have some of the friendliest, least pretentious, indie/underground/interesting-music-knowledgeable staff around. JENNIFER MAERZ