While I love to help open source communities by mirroring mailing lists, I can't deny the fact that it costs me money, too.
There's the cost of server capacity, bandwidth and dealing with takedown/removal requests. I don't mind paying for these costs myself, but as the traffic to this site grows, so does its cost.
As a result, I've set the following rule: all posts older than 30 days will have ads on them.. These are mostly Google-hits for people searching for very specific content and finding it here. Since it most likely helps them out, I feel less bad about showing them an advertisement.
On the other hand, most traffic comes here via social media for 'hot announcements': a new security vulnerability, a major new release for a project, ... Those high-traffic posts are usually the most recent ones. They will not get ads.
The idea remains to browse those post in the most enjoyable way possible: clean, responsive and with a keen eye for typography.