Enact member reputation grading / filtering (so I can set a photo to only be viewable by people with at least a grade B reputation, for instance).
In order to be eligible for reputation, a member's account should be at least 2 weeks old and he should have at least two photos viewable by anyone. After two weeks and as long as two photos are available, the member accrues points based on the number of noms his status messages and replies to others' messages receive.
Allow admins to dock or reset a member's reputation to 0 if they are warned about something.
BONUS: if a member creates an event, he will then have access to an RSVP list of all members who indicate they will attend. The night of the event, when a member is in attendance, the organizer will be able to check off that member from the RSVP list, awarding each of them a very generous helping of reputations points.
One particularly great application of having reputation is that you can build out Content Flagging Mechanisms.
If there are trouble-makers on the site, (nudity, spam, etc), then each member that flags that content is essentially putting their reputation behind their report. When enough reputation weight has flagged something, then the system can automatically manage hiding it from all users (or blocking a spammer/phisher), without needing to wait for an admin to manage it.
It goes without saying that any member caught unjustly reporting someone else could be penalized by having their reputation docked by an admin by an arbitrary amount of points. This would prevent members from flagging someone they have a dispute with.
The simple way to do this is max out reputation at some number (100 or 1000). Once you hit the max, you've got an A grade and that's it, you're done (requires not assigning grades to anyone until at least one person hits the max though!)
The complicated (but potentially more useful) way would be to have no maximum score, grade on a curve, and automatically age reputation:
Every month, a member who has not logged in would lose 10% of reputation, down to 10 points. Thereafter, lose 1 pt per month until they hit 0.
Members who are active would lose 0.5X% of their reputation, where X is equal to their reputation percentile expressed as an index of 1 to 10. So if you're at the top of the reputation scale, your index would be 10. You would therefore lose 5% this month.
This way, new members are always able to catch up and the playing field would constantly be self-leveling.
An interesting twist would be to make reputation for attending live events protected and unageable. I'm pretty sure that's a lot more complicated than anyone wants to program though ;)
A third approach is sort of a hybrid method. Use hardcoded point thresholds/milestones for grades (i.e.: 100 or 1000 for A)... yet still allow points to accrue indefinitely. So John could have 1000 pt and Greg 10000, but both would have an A.
In this approach, the grade is used for filter behavior as stated in the original proposal, while the raw score would be useful for determining other behaviors (perhaps granting moderation privileges, or running a contest... anything). The raw score need not be exposed in any case.