I use inkscape, and I really like the feature that lets you use the paint bucket on your line work. It makes the line expand a little bit, but by doing so it also smooths out any irregularities in the line work. The result looks very nice.

I was wondering if any other programs have this feature? Is it common for vector programs to have it?

Adobe Illustrator has a feature called "Live Paint" that does the same thing but doesn't affect the line size. You can even paint a line away if you wanted.