OK, so I tried worldgen on the Linux box at home. Huge difference, and not for the better.
The Linux box at work has 2 GB RAM and a fairly recent CPU. World gen took somewhere between 5 and 10 minutes, I think. I didn't time it.
At home, I've got 1 GB and an older CPU (Athlon 64 3400+). World gen using the default parameters took between 15 and 20 minutes, I think -- and at the very end, the memory usage shot WAY up, to nearly 1 GB virtual size. My poor machine started thrashing, which means it took ages to accept the world and get it saved. (I have a lot of other things using memory too, including a web browser.)
The region directory is also about 5 times the size of a .12 region directory (100 MB vs 20 MB).
After saving the region, I quit the program and re-launched it. When I selected the region to start playing, memory usage shot up again, just like before. I allocated points and skills and stuff, and embarked. When the dwarves arrived, I saved and exited again, then restarted the program.
Same memory usage -- 1 GB or so. It's pretty bad.
However, once the game finally loaded, the memory usage seems to have dropped off. Virtual size didn't drop of course, but the resident set size dropped to under half a GB. It might actually be playable, but I'm worried that seasonal autosaves are going to be a right bitch.