Travel rants has a good article on the trade offs on using different channels to book travel. see Direct Bookings
Travelers have moved dramatically to direct bookings over that last few years. The split is now slightly in favour of direct bookings and seems to be stabilising there.
see a full discussion on this at hostipality biusiness (merrill lynch survey)
The main reasons:
They deal with the owners and host of the place they will stay.
They get to know them and
more importantly they get to be known.
Dealing direct means they have better control of the itinerary, its easier to change dates and get upgrades etc. Its easier to correspond - to ask questions about the destination, activities and things to be wary of, and it from the horses mouth - so to speak.
it sued to be that middlemen had the edge on package holidays - but no so now. With hotel tools, travelers can actually create a vacation package on sites like http://realholidays.com and still deal direct with the hotel. These same tools are being used on hotel website to allow users to add activities and air to their package.
Travel tools used by destinations and tourism sites such as; hotels and activities are making it easier for us travelers to get what we want and how we want it.