TripAdvisor is pushing the "fees estimator" as a key selling feature... This handy item allows users to calculate the full cost of a trip including baggage charges. Somewhat humorously, it also will estimate on board charges - even down to if you want a cocktail. But, the fee estimator only appears to work for domestic tickets in the US.
See full story at http://hudsoncrossing.blogspot.com/2009/02/tripadvisors-kayakflycom-knock-off-goes.html