Fifth Avenue. Rodeo Drive. Avenue des Champs-Élysées. Event the most acclaimed retail strolls in the world have not escaped the ravages of the global economic crisis, according to Cushman & Wakefield's annual Main Streets Across the World report. Surveying 274 leading shopping streets in 60 countries, the real estate services firm found that 54 percent of the group experienced a decline in rents; a decline that marks the largest drop in retail rents ever recorded since the report' s inception 24 years ago.