I do all my 'digital' maps in Visio - mainly because I'm a rubbish artist. Yes, it can give you a very 'clinical' look and you don't get anything like the lighting efects that make a building drawing (as opposed a plan) look more interesting, although if you use transparency on say, a yellow circle you can get a rough version of the same. Shading is rudimentary, but as Fujisawa Rob says, you can use imported textures to reasonable effect.
Fujisawa Rob is right in that it won't do jagged outlines, but I've had reasonable success doing contour lines with the freeform tool. You can get a good-looking, scale plan in a fairly short amount of time - especially if you re-use parts of your previous work. If you do any 'technical' style work - such as spaceships, etc. then I reckon it's a good investment, especially if you are eligible for a student discount edition or can get an older version cheaply.
A couple of incomplete Visio maps for "Return to the Keep on the Borderlands":