I don't know that it really depends on geography, but the chances are pretty good that any two randomly connected nodes might not be able to see each other. Even if you both connect to the same host cache, so many people use it that you may not be able to reach the other person (especially if you connect at different times). It's all the luck of the draw.

As the gnutella net grows, it becomes harder to see all (or even most) of the nodes on the net. The best solution is to have the person connect directly to your IP address (or you to theirs).