looks like on the new Y! preview home page, if you go to travel, then the search box segments to travel listings only..
in theory, segmented listings seem like a reasonable idea.. however, this seems like it's 1) just a bunch of ads and 2) only listings from the Y! directory with little search relevance compared to the regular SERPs..
yes, it seems pretty useless at the moment. it appears that Y! is trying to apply the same type of segmented search to travel as they have done to tech, where you can directly find a product (such as a digital camera) and make a purchase. for travel, they have added an AJAX based add to trip feature. however, travel is not bought and sold the same way as gadgets so it remains to be seen how useful, if at all, this feature will be (except for Y!'s advertising revenue of course)