Statistical Analyzers for HTTP Logs?

krishnaD asks: "I have been using webalizer to generate access log reports for the site but lately my customers are asking for statistics like average amount of time spent by visitors on site, if a person reaches a page X, what is the probability that from here he goes to Y? From which link people exited the site etc. Basically, they are asking for a detailed flow analysis of usage patterns of visitors. Are there any tools that will do this kind of analysis? I love to know what kind of tools other sysadmins use to generate reports for their clients."