Like September's Republican bacchanal or the American Atheist Society's convocation at the downtown Marriott back in March, most of the conventions the Twin Cities accommodate are onetime, fly-by-night affairs. No sooner do we fall in love with the visiting horde then it vanishes with nary a "see ya." But every Fourth of July weekend, the decade-old, nonprofit-run sci-fi and fantasy CONvergence offers distinguished speakers. This year's guests include Blade creator Marv Wolfman, Peter "Chewbacca" Mayhew, and fabulist Mercedes Lackey, to name but three on a very long list. Also on tap: panel discussions, screenings, DJs, a costume contest, masquerade ball, and live experimental music in the black light-bathed Connie's Space Lounge. Which is only part of why the Sheraton Bloomington Hotel is already sold out for the event's duration. Nowhere in the metro, ever, is mundane reality so thoroughly held in check for 48 hours-plus.