(Note: I originally posted the following in response to this post at The Long Tail blog.)
"Many" and "most" are among the most over-used words in the English language. Some readers glaze on past these words, assigning neither any meaning. Depending on the context and the reader, some readers take "many" to mean most.
"A large number of" and "the majority" are overused, as well, as they are used to avoid repeating "many" or "most" within paragraphs. The better approach for the writer or speaker is to seek out definite percentages, numbers, or proportions. Even better is to avoid writing oneself into the position of having to use one of the imprecise terms or a synonymous word or phrase. Writers would do well to search manuscripts for occurrences of "many" and "most," and then go back and write them out.