I get asked this a lot. I also get asked 'Did you get one of those around the world tickets?'
Well, the answer to both questions is no. We haven't booked the flights that are at the end of our trip - for the simple reason that they are a bit too far to book. Everything else IS booked and it has been a great learning experience to research the best way to do this.
Hint 1: Round the world tickets are not a great idea if your trip spans several months. They seem to work better if you are planning a honeymoon type 'around the world in 4 weeks' thing. In any case, you are generally looking at upwards of USD 5,000 per person.
Hint 2: Forget Expedia. Or maybe not completely, but you should see it for what it is - a money making travel behemoth. Many budget airlines do not sell through Expedia.
Hint 3: Read backpacking websites. Backpackers are geniuses when it comes to making your money go a long way (pun intended). One of my favorites is 'Nomadic Matt', and he recommends Momondo as the number one flight search engine.
Hint 4: Then spend many nights clicking on meta searchengines such as Momondo and Skyscanner. I specifically grew to love Momondo as its system of rating the flights is so great (see below: Cheapest / Quickest / Best). When all three are the same, you hit that smiling face and score a perfect 10 you know you found a good flight. Compare, check numerous dates - and then book.
Is all this effort worth it? I think so. My first overall flight budget for this trip was $20K. We ended up at $13K. And that is for three people. In Canadian dollars. We have 14 flights of which two transatlantics we fly on points. Only two of the flights got booked through Expedia.