Well, I was thinking about continent shape, and I drew up a basic map that would have some main areas sketched out. And, for the record, I think it will work no matter WHAT 4e is, because if 4e can't support something this generic, the game is broken, and I'll stick with 3.5E.
At the bottom of the map, we have an antartic landmass, covered in ice. Much of it is like antartica, except for a thin peninsula of land that juts up. This peninsula would be home to Viking-esque raiders that war with one another, and raid nearby landmasses. I also think some other "ice barbarians" would be nice. I think inuit-style hunter/gatherers on dog sled would be fun, to the extreme south.
We could then fit in a chain of islands, probably mountainous, that we'd leave open for GM expansion. I was thinking it'd be neat to put dwarves on this island, although explaining dwarves in detail should probably wait.
Then, we have a fairly small continent (australia in size?), with the southern parts being temperate, and then sub-tropical, with only the northern tip being tropical in any way. The western part of this is fairly humid, and then we have a mountain range, and everything east of the mountain range is at least sub-arid.
ON the western shores of this continent, we have the main cities (a collective of three or four cities that ally themselves as a confederacy) and an empire on the northern tip that is at least mildly evil (they keep slaves, and may have some evil magic things going on - they used to control the whole continent, and they want it back). In the arid regions, we have a large grouping of people who live in city-states, with each state based around an oasis, as well as an arab-like people who run trading missions between these city-states. We could also fit in a farming people along the shores of a wide river cutting through the desert (preferably in the northern area).
Then we have an archipelego system, with many different cultures on the islands. This is where our travel comes down to - it's very easy for a GM to invent an island, but we can always add enough big ones to attract idea-strapped GMs. And I like the variable travel rules - personally, I think it'd be neat if we had a travel god or goddess that mariners would pray to before they sail, out of a hope that they can avoid the "mists of travel" or whatever they're called.
Finally, to the north, we have a large landmass (like asia), that's covered in jungle. Only a few parts of this are civilized - the rest are filled with all sorts of ivy-covered ruins, festering swamps, and violent volcanoes. In other words, a great place to set an adventure.