An urban renaissance took hold in the boom. Elegant towers planned for city centers lured baby boomers to live in style. They blended condominiums, shopping centers and offices under one roof. But the bloom is off that rose now in most all but the biggest cities — and even there it's not as sweet. The housing bust slashed condo prices and left a glut. Recession drove unemployment over 10%, slackening office and retail space demand. And a credit