From the ascendance of the reference database and web sites offering endless opportunities for cyber-promotion to the crowds swarming through the doors to avail themselves of new computers, the Internet has transformed the way public libraries do business. That is not news. What is exciting, though, is how the Internet continues to change public libraries, even if, at times, it can be a double-edged sword. Take circulation, the success story of "Library Journal's" annual book-buying survey, which began in 1998. According to the survey, a snapshot of a select group of public libraries (the "Library Journal" 100) distributed evenly throughout the country by size and type, circulation has been flowing upward since a slight dip in the late 1990s. This article reports that just over half of this year's respondents report an increase in circulation--almost as good as last year's 55 percent and appreciably better than 1999's 32 percent--and circulation rose on average by over four percent, the survey's biggest leap yet. (Contains 3 tables.)