I don't know if there's a limit, but whatever it is might make finding what you want difficult. My wife had a huge number of compilation CDs, including some quite large sets, when we merged our CD collections. When I came to rip them to the B2 I set up a load of "Various" folders with sub-titles based on sets, such as "Various - Brit Awards" as well as more obvious genre sub-sets like "Various- Classical Guitar" and others like Christmas and film/TV themes. It certainly makes things easier to search.