Only in Las Vegas could there be fretting over the fortunes of the city's biggest industry after a banner year filled with record performances. But it's true. Even though more people visited Las Vegas in 2007 than any year in history there has been a parade of experts who say we may not be as fortunate this year. It started with Preview Las Vegas, the annual event sponsored by the Las Vegas Chamber of Commerce and the Nevada Development Authority, two organizations notorious for their bullishness on the local market.