AppleTV1 had an advantage with a built in hard drive to sync media to and no need for an internet connection except for new rentals/authorisation of downloaded ones.
While AppleTV2/3 seem ideal for travel they are dependent on ethernet or a wifi connection with a defined network name and password to connect. Many places where internet is provided by a web based login are not usable unless you can internet share via a laptop or have a mifi type device.
As many places I've been to in UK recently are out of wifi or 3G range I've opted to take a Mac Mini and AppleTV connected to it to play from itunes. I naturally lose internet based rentals/Netflix etc.
Indeed, AppleTV2/3 doesn't hold any content. On the other side, the fact that you can now stream from any iOS device mean that you probably got your content with you anyway.
I agree that a geek traveler will need to bring along with its AppleTV2/3 an AirportExpress and an iOS device (or a laptop). If you want to travel light, it's probably more convenient to simply bring a cable adaptor to plug directly your iOS device to the big screen.
I wouldn't dream of carting my ATV1 anywhere as it's way TOO heavy and too big. And IF you need to leave an ATV2/3 due to size/weight, you're really going LIGHT.
The rental unit we're staying in for a month has good throughput. Otherwise, the ATV2 would be mainly useless. I think I did read that the ATV2 had about 5 MB or a little be more storage so it should be able to download at least one movie for continuous streaming. If the pause whirly is spinning, I don't want to watch it.