Sorry, it seems it's a bit of a false alarm; the package maintainer just contacted me saying he'll abandon it himself. On Tue, Nov 6, 2012 at 4:20 PM, Mike Swanson <mikeonthecomputer@gmail.com>wrote:

https://aur.archlinux.org/packages/freenet/

The maintainer has not for many months about bad checksums and a user's request for a systemd service (which was provided in one of the comments too!). In addition, he has another package flagged out-of-date since July.