Having just traveled around the world over 7 months but NOT freelancing, I would have to say that:
* net connections are very very spotty,
prepare to work offline
* supplies are rare (usb devices, upgrades, etc),
expect to pay more for less
* desk conditions are poor, rarely did we
find a place where I could get into the flow.
Checking email and noodling on the net was
fine, but getting real quality work done
requires spending time to find the right location.
I think it could be possible, I have written some of the best code of my life in a corporate budget hotel holed up for a week with only a 1Mbps internet connection.
You can simulate work/travel by playing with IPFW settings on your mac and only working out of a macdonalds.