Many Las Vegas casinos have lengthy customer lists built up over years in the business, as well as a fine-tuned sense, after years of trial and error, of what customers want. Not the M Resort, which opened March 1, in the worst economy in the modern casino era. In its first few months of operation, the M, at the southeast corner of St. Rose Parkway and Las Vegas Boulevard, saw revenue soar as thousands of customers took in the property, hailing its modern yet comfortable design and reasonably priced gourmet restaurants.