Here we go:

• Readers enjoy lists because they get straight to the point, they’re an easy read.
• Lists can provide large amounts of information in a small number of words.
• Lists are easy to write. They do not require any complex compilation of writing.
• Lists do not take long to write, for the same reason as above.
• It is easy to add items to a list
• Social Bookmarking websites, notably Digg absolutely worship lists, they can provide an orgasm of traffic.
• It is not difficult to make a list that has not been made already.
• People love referring other people to lists.