Then you're gonna love Google Flights:

http://flights.google.com

Powered by ITA's backend.

The obvious thing google flights misses over ITA is the month-long search option, which I use a lot. For the power users, ITA has a very useful regex-like syntax for specifiying flight queries, but that is understandably not of as much interest to the vast majority of people

I live and die by the "advanced routing codes" on Matrix... see my previous post here:

     SFO,LAX CX,AA,KE F HKG,ICN,NRT ~CZ+ KMG

http://news.ycombinator.com/item?id=3090362

Google Flight Search has a calendar view: it's hidden behind the button directly to the right of the return date and lets you play with different departure date and trip lengths.

"Sorry, locations outside the U.S. are currently not supported."

Well, I'm sure it's a very nice interface.

Yeah, I just tried to search a flight to a European country and it said "unavailable". So it's not accessible from the US to the outside either.

It takes time to support all the airlines in the world. Give it a few months...

No, it doesn't. Every major airline publishes their fares, schedules, and availability in a standardized format; furthermore, all of this data is available from a single collection point. If Google wanted to allow international searches, they (or more importantly, ITA) already have everything they need.

They quite literally just need to "flip a switch" to enable it.

Most likely the reason they don't is that each additional origin or destination city that they add requires additional servers and storage and computation, and so it's much more practical for them to limit the tool to the top 50 or so Domestic USA airports.

Not so much.

If you've used flight search, you'll have seen that it's instant response. Change a filter on price, length of flight... anything... and the results instantly change.

The results are pre-computed... thus extending it to international flights is far from just "flipping a switch". It makes the pre-computation 1-2 orders of magnitude more difficult!

Thank you for this info very useful. Where/what is this "single collection point"?

The schedules come from OAG, the fares come from ATPCO, and the availability (number of seats available on each flight in each booking class) comes either directly from the airline or through one of the three GDS providers: Sabre, Amadeus, and Travelport.

Technically, the schedules and fares are also available from the GDS, but only in an interactive format. ATPCO and OAG supply giant dumps of bulk data which is more suitable for offline processing and precomputing results.

ITA backend supports them already (e.g. see the matrix site), it's just not as fast as Google flight search.

I've been a confirmed Kayak fan.

I don't need to go anywhere at the moment, but you comment got me to try a search on Google Flights. Let me just say, Wow! Simplicity, organization, speed!

Of course, the true test will be when I do have to book. I'll be sure to try 'em both out.