I've hacked a local_scan function for Exim lately. The purpose was to be able to use the Distributed Checksum Clearinghouse system through the dccifd daemon rather than to call a dccproc process for each mail.
The code isn't certainly perfect, but it seems to be working rather well and I must say I'm pretty impressed by the efficiency of DCC.
On another subject, my IPv6 tunnels seem to be very popular. I already have more than 25 without doing any kind of advertisement. Time to start doing some serious scripting about it. I need something a bit more automated than what can be found on http://www.physicman.net/tools/
In the mean time, I'll continue to build some Debian packages.