hey, i just came back from a one-year RTW and just did my accounting. result: 21,450 Euros.
i had roughly budgeted 18k, but giving myself a margin of 3k, so i'm in my budget basically.
i'm not a geek unfortunately, i just tried to note down my expenses in a little notebook, and basically every three-four weeks would check how much i had spent in average per day, and would adjust my spending accordingly. i had estimated roughly 35 to 40 euros per day, and ended up with total spending of 46 per day. but i never said no to anything because of the cost. of course, i always stayed in dorms/hostels or couchsurfed, ate mostly in cheap joints, but the big spending was in entertainment: skydiving, excursions, treks, diving, massage course, and... concerts!
i wish i had had the same approach as Going Global, separating the "everyday" spending (food, lodging, transportation, etc) from the activities. the other thing i wish i had done was to prepare an estimate of average daily spending per region of the world. it's so incredibly different from Asia to OZ and NZ! in VietNam and Lao, i spent about 25 euros per day, and in NZ, 86!!!
but in the end, even though i was slightly over budget, i don't regret anything, and i didn't worry too much about the spending, i was just "worried" about having a good time, knowing that if i went over budget, it would be just slightly, since i remained relatively reasonable. my advice would be this: make a rough budget, check it often enough so you don't have bad surprises, and just have fun :-)