Here are some facts:
1) Game Masters love making dungeon maps.
2) Players hate making dungeon maps.
Because of this, GMs end up with wonderfully complex maps that, once translated to the player's minds, are just some boxes with lines between them and a few notes. The Cartography skill from HM5, in this case, is pretty weak.
Things to Do with Cartography (in the dungeon)
If a character with cartography has made a map (i.e. the player has made a map) then a cartography check can be made to do a few things if the character takes a moment to study the map and their surroundings:
1) Determine best known path to entrance (-10)
2) Identify places previously mapped (+10)
3) Notice strange construction/paths (there should be a room here, or I think this passage doubles back on itself) (+40)
4) "Connect" mapped areas (+10)
5) Get a hint (see below) when at an intersection about where a corridor may lead (limited)
In addition, player who has a character with trained cartography can ask the GM to map one area, review some piece of their map, or ask a yes/no map-related question a number of times per session equal to their rank (novice = 1, average =2, etc).
Make MapsCool, Not Technical
Mapping should be kind of fun and not tedious. Who cares if the room was 20x20 with a 5' alcove in the north side of the eastern wall? What players are interested in is that in a moderately sized room an alcove beckons them - a strange mist seeming to roll from the floor and an ominous grinding noise coming from beyond the far wall.
What is important for the GM to do when mapping is make the exploration interesting. Multiple elevations within the same level, multiple paths, that sort of thing. Straight line dungeons are BORING. Read This.