6 months fine. But what about 12, 18? What about when Maemo 7 is out and his helpful little utility either doesn't compile or isn't used?

No-one's suggesting that everyone has to release a new mega-app every day to maintain their karma; and there are fundamentally hard technical issues with implementing it (every time I've raised it and pushed for it, it'd require a fairly hefty rejig of the way karma is calculated[1]).

However, say you lost 25% of your karma every 18 months. Obviously if you're still active in Talk, Bugzilla, Downloads, Packages, Brainstorm, the mailing lists you'll not go down that far - and may even go up. But it'll prevent a static list of people in the top 10.

The point of karma (crudely) is to measure a person's value to the community at this point in time. There's no point rewarding someone for work they did on the 770, if they've done nothing since OS2005. If nothing else, if they released it and were still supporting users of it in Talk, and it still got Downloads, they'd still be earning fresh karma.