This is maybe a rude question, and if so please forgive me because it's entirely not intentional.

I'm interested in doing something like this, but the sheer cost of the flying, the time off work, the hotel costs, etc. makes it seem cost-prohibitive. Any secrets to economical travel, other than a healthy piggybank?

I find the three big costs are transportation, accommodation, and food.

We got several quotes for the flights and ended up going with a travel agent that had a "best price guarantee" which saved us a bit. They also gave us an extra $100 voucher for going with them that we applied to a rental car. We booked at the very end of January which I think helped grease the wheels as they were closing out the month (this was unintentional). Various airlines also have more flexible "round the world" fares where you don't have to book exact flights ahead of time. These are surprisingly cost effective, and even more so because the airlines offer wildly different prices depending on which country you are in when you buy them. I talked to somebody once who flew to Egypt and then bought their RTW ticket there, and saved heaps.

Land travel is obviously less overall cost but it can add up. Figure out the local public transport where possible, instead of using taxis (unless you happen to be in Peru, where the taxis will take you across town for 3 soles, or about $1). If you choose to get a rental car (which gives you so much more freedom to explore in non-urban settings) that cost is unavoidable but often worth it. No way I would get a car in an urban area such as London or Tokyo, that would be crazy.

For accommodation, youth hostels are a good choice. Don't be put off by "youth" in the name, you'll find all ages of young-at-heart people there. Some countries are better than others for this, but you can often get a bed for $20 or less. Shared accommodation (bunks) is certainly less than a private room. More work but even less cost are options like CouchSurfing and Global Freeloaders where you can stay with locals. Book your first night at a reasonable-looking place in a new city ahead of time because it's so much easier to choose a better place once you're there (also, most countries prefer or require you to have confirmed accommodation at the border crossing).

Eating out continuously is seriously expensive. Find a local market or grocery store where you can get small quantities of fresh stuff to eat on the go (sandwiches, fruit, bread, snack bars, etc)—stuff that you can eat anywhere that doesn't require cooking. Most hostels will provide shared kitchen facilities, so you can cook up your own food if you'd like a more substantial meal (pasta is a good cheap choice). I've even seen people have just porridge twice a day but that might be pushing it! If you do eat in a restaurant and you're travelling with somebody, share portions. You can usually get a better deal by getting a starter and a main and sharing both, rather than two main portions.

Regarding time off work, we're lucky here in New Zealand to have four weeks vacation time per year. This is for everybody, and is required as part of employment law (it was increased a couple of years ago from three to four). I've been saving up time off in anticipation of this, and although I'll go a bit negative by the time we're back, my employer is very flexible about days off just averaging out over the long term. I put in my vacation request well ahead of time so we could work around it in terms of project planning.

I try to do a travel budget (just a simple spreadsheet) before leaving just so I have a clue how much I might be spending. It usually turns out to be a bare minimum, but it's a good reality check anyway.

Wow, this turned out longer than I thought. Hope it helps!

Thanks!

A few years ago, a Round-The-World ticket from NZ was US$1000 cheaper than from the US. (I want to say that the lowest option was US$3000 in the US and US$2000 in NZ.)

I was in NZ and had a return ticket to the US and work wanted me to make a stop in India. It was the same price or cheaper to get a RTW through India than to get last-minute flights to India and back to NZ. So I paid the fee to reschedule my return ticket for later in the year and then booked a RTW for Delhi, Berlin, Boston. Then took the final Boston to NZ later in the year and finally used my original return flight. So I got an extra trip to NZ out of it (for the price of the reschedule fee).

I find it humorous that the map looks kind of like an orbital map for something around 60 degrees of inclination (like the ISS).