Been using Expedia for 14 years, though not exclusively. Contrary to the post, they often post discounts unavailable elsewhere, particularly for combos. For example recently, the regular rate at Wynn Las Vegas was around $200 a night in December but with an Expedia flight it worked out to $140 a night. This is the discount they usually give their mid level Red Card members, if I recall correctly (upper get RFB).

I've also used Expedia to book a stay in Cancun a few years ago; they had a number of mom and pop hotels listed with rich details, but Ultimately I got a great combo rate at the Ritz Carlton (like $240 - it was about a week before the season really began); this rate was not available on the Ritz website.

I have had some bad experiences with Expedia when requesting refunds or changes, though this has improved over the past 2 years with more software features and slightly better call center agents (ymmv).

Ultimately I'll book direct with the hotel or airline if I have a specific reason to (schedule, FF points, upgrades, etc), but for easy price comparison and research I tend to rely on Kayak and Expedia almost exclusively.

This posting has not changed my mind that they offer a good service - they seem to have issues with their Latin American offices.