Well, this is something that I (everyone) should do if the line-work sucks.
I'm guessing that cartographers who have a background in graphic design would automatically redraw all line-work...while those with a background in GIS would accept the lines as is, for whatever reason (perceived accuracy, etc). I redraw boundary lines on smaller maps, but rarely on a large one.
Cartographers with a background in cartography will probably redraw the shore lines as well.
It's not really about completely re digitizing anyway, a lot of what makes illy so powerful as a map design tool is how it handles lines for you and there's a lot you can do to improve the look of an Arc imported map with out actually redrawing.
Leaving lines raw for accuracies sake is, in many cases, pointless (especially for road or water features). The scale of the map will determine the degree to which you can safely generalize without affecting the users experience in terms of accurate reading. In most cases, even at large scales the raw line work is being printed or displayed way above that threshold where small changes in appearance actually change the data location beyond already existing error margins.
Not to mention the fact that data came out of a GIS is in no way a guarantee of its accuracy. There can be a lot of slop in the way this data is created.
My current work flow looks roughly like this:
1) Use map publisher to directly import base shape files for map layout (nation/state borders, continents, shorelines, roads, hydro, point featres etc.)
2) Create shaded relief in Natural Scene Designer; process through Photo Shop; import directly into illy via MAPub
3) Use MAPub selection tools to parse raw GIS data into usable groups and new layers (eg separate mass tangle of hydro linework into groups of rivers and streams by stream order, or stream flow, or name etc. or use MAPub to select desired road system info, and join on name or feature classification etc.)
4) organize layers and features into logical hierarchy and start applying spec changes to create the finished map.
There's a lot of little unwritten steps in there of course but that's the general work flow. 99% of the time I can get away with using just MAPub to do all of the GIS work, it's really more than just an importer and can handle some heavy lifting in terms of parsing data. I go to my work Arc software to do the few things MAPub can't do, or I don't know how to do (like clipping).