What do you mean the forums are dead, they are livelier than ever.
Andrew, the forums are very quite nowadays. I joined back in 2006 and although I don't post a lot I do subscribe to the RSS feed so I get to see how much activity there is on a day to day basis and how it compares to the past. I'd say in the past 6-12 months the activity has dropped a tremendous amount from say a year or so ago.
One of the things that bring people to the forums are new releases of the software and due to the way Terragen is developed sometimes there are many months between versions. They don't tend to do small incremental updates or beta releases, well not public betas anyway, so I think that has a big impact as well. Also there doesn't seem to be as much picture posting either, not sure why this is.
Hopefully the winter months will bring back some more activity, lets see....