Ok, so fooling around on orkut gave me an idea: Is there a way to incorporate social networking into arcade style gameplay?
The simplest way to do this would be to reward players for making friends and for making groups.
Here is what I came up with:
Imagine a platformer in the style of Mario or Megaman. The need here is for levels that you can finish, but you can also go back and play through it again and find new parts, or branches.
You get a charactor1 that has 4 attributes: Strength (jumping power), Air (lower falling speed), Defense (healing), Merge (pass through barriers). Your charactor starts out at level 1 in each attribute. There maximum level you can get in an attribute is 9. The levels contain single-use powerups that immediately increase an attribute level, but wear off. The levels also contain "filling stations" where you can replenish particular attributes.
Your charactor can play through the levels as expected. There will be some (undefined) mechanism for your charactor to go up levels, but on his own, your charactor can only gain 6 levels, and no attribute can have a level higher than 3. If you only want to play single-player, this will be considered the end of the game, and the player has won. 2
At this point the charactor will have 9 points distributed among his attributes.
You can also play through a level with another player. When you do so, the goal will change. The goal of the level will be determined by your combined levels. It might be something like "both make it to the end with full health" or "both make it to the end in X seconds" or "find a path to secondary objective". It should be necessary to use teamwork to acheive the goal.
Upon sucessful completion, your charactors will become "friends", and your charactor will go up one level in the attribute that his new friend is highest in.
To advance, a charactor must make at least 6 distinct friends. At this point he will have 15 points distributed among his attributes.
After this, the charactor can advance up to 24 points either by making new friends or by achieving more difficult goals playing solo. However, the charactor cannot go beyond level 6 in any of his attributes.
8 more points will be available to a charactor by joining a groups. Groups can be created arbitrarily by any player. When created, they must specify which attribute the group will focus on.
Any charactor can request to join any group. Groups then accept requests via some (undefined) mechanism. A charactor can join as many groups as the player wishes (although there is no functional reason to join more than 4 groups).
When the group has 6 charactors that each have level 6 in the group's focused attribute, ALL members of that group will go up one level in the group's focused attribute.
When the group has 12 charactors that each have level 7 in the group's focused attribute, ALL members of that group will go up one level in the group's focused attribute.
So via joining groups, a charactor can achieve 32 points.
There is one more point that is available to charactors. Because such a game requires many high-quality levels, a group that contributes a good level will get a bonus point in its focused attribute.
There will be some mechanism for ranking the quality of levels. And the extra point will only last for a month or a couple weeks or something.
I'm working on another game right now, but if you're interested in this idea and can program in pygame or make graphics, I could probably be talked into following through with an implementation.