Interesting. I did my Wheel of Time map in CS3 and used the Pencil to trace the entire coastline without problem. I'll have to look into it once my computer is set up again and see if I can find where the limit is.
It's also possible that it's a memory issue. I have 12 GB available, so I might not run into it if CS3 was 64-bit. I don't recall if it was or not. I know Photoshop was, but I'm not sure about Illustrator.