I experienced and solved this problem myself, so I figured I'd post something about it in /r/minecraft in the small chance that someone else is having the same problem.

I was able to run around most of my world map in hand with no problems, but when I hit a specific area, I would get kicked out of the server with an exception. Avoidable, but incredibly annoying.

After a massive amount of trial and error as well as a narrowing down of the problem area, I decided to comb the "epicenter" for things that could screw with map creation.

After a bit of searching, I found that a diligent worker on my server had apparently dug a hole straight down, through a hole in the bedrock, and into the void below. This small block of empty map that led all the way down to the void was the culprit in map crashes. I filled it, and immediately was able to map the area with no problems!

Hope this helps someone, although I'm sure Notch will put out a patch fixing the problem soon enough.

Tl;dr - If your map is crashing in SMP (and possibly single player), look around the crash area for a hole to the void. Fill it, and the crashes should stop.