In Diplomacy tournaments I've played in, points are awarded based on placement, and not on number of units left in the game; i.e., first place gets X points, second place gets Y points, etc.
In this system, usually first place is divided up among multiple players for a shared win; solo wins are quite rare. In such instances, each member of a team gets an equal # of points, regardless of how many units each member has.
The only different points system I've seen used had a rule that either it was a solo win and winner took all, or else every remaining player on the board received an equal share in the win, even if you only had a single unit left. In that system, solo wins got a certain # of points, and a shared win got a percentage of that # based on how many players were left in the game. (With three players left, each got 1/3 of the total points awarded.)
I've only played online diplomacy here at phpd. What kind of point systems do other services use? I've heard of dipbounced and a few others, but never tried them, as they seem too complicated in comparison to phpdiplomacy's simple interface.
Please note that I do not recommend either of these scoring methods for phpd. Points here are more for the benefit of the community, and so you don't want to rob people of hard-earned points. What I've described above are point systems in tournaments, where it is okay to screw over losing players by awarding little to no points. So don't think I'm advocating change. At least not to a tournament point system.
Although I will mention that in the past, before the point system was implemented, I had a habit of joining games under civil disorder where I could make the last couple of moves for a country with one or two units left to be intelligent rather than just sitting and holding. I thought this was a benefit to the community, because it made civil disorders that were sure to lose more active countries, rather than simple passive holds. But as a result, my points rating was affected quite negatively once the points system was implemented. I would definitely like to see a modification to the points so that countries where there is no chance left to win can still be entered without hurting your points. Maybe an option to join for a fifth the price by foregoing your chance to win anything in return? Then you might join as a civil disorder country just to play is last few turns without feeling like you ruined your points score because of it.