Anyone wondering when gentrification will have officially and completely taken over Williamsburg should mark Saturday on the calendar. That's when '90s Fest, a nostalgia-soaked bill more typically found at suburban amphitheaters, makes its way to 50 Kent. In case you've been too busy with jobs, kids and a mortgage to keep up with your old favorites, here's what you need to know before you dig the flannel and cargo pants out of the attic.