A look on the registration-counts of new users reveals a big peak between 2005 and 2008 of 9000 new users per year, which I guess also played a lot per capita.
| Year | RegCnt| Active |
| 2001 | 227 | 39 |
| 2002 | 1470 | 94 |
| 2003 | 3625 | 155 |
| 2004 | 5512 | 176 |
| 2005 | 9099 | 244 |
| 2006 | 9862 | 212 |
| 2007 | 9613 | 218 |
| 2008 | 7526 | 222 |
| 2009 | 6139 | 185 |
| 2010 | 5983 | 274 |
| 2011 | 8597 | 323 |
| 2012 | 7897 | 401 |
| 2013 | 5675 | 516 |
| Sum | 81225 | 3059 |
Between 2006-2007 there was one user (Razorflame) which raised the running-games a bit by playing 1500 simultaneous games, which most over the next years timed-out because he couldn't play so much. So you can count one 10%-block of running games (which is about 2000 games) to that user alone. But the long decrease down can not be attributed to one user alone of course.
I can only speculate about the fall between 2007-2010: less users registering, perhaps doing other games/activities, using other servers, or just playing less games, etc.
Same goes about the rise between 2010-2012, which I can't explain without guessing about reasons for an increase.
In 2012/06 there was a server-upgrade with many new features, that increased the server-load of an already slow server further.
Additionally between 2011/03-2012/05 the number of RSS-requests were increased ten-fold from 1 Mio requests/month to 11 Mio (compared to ca. 2.3 Mio game-page requests/month that didn't change during that time) by polling RSS too often, which added to making the server extremely slow. The server back then had only 1 GB memory and we later found out, that because of that there was a lot of swapping with a lot of disc-I/O.
So during 2012/06-10 the server almost became unusable with a lot of max-connection-problems and net-timeouts. Because of that I think a lot of users played less. This could explain the steep fall till Oct-2012, which was abruptly stopped after a new and much faster server was sponsored and installed by the DGS-provider.
Also (like ez4u said) in the server-upgrade in 2012/06 the default time-limit was indeed changed (from Jap-byo-yomi 90d + 10x 1d to Fischer 30d + 1d). I agree, that this could be an explanation that let players play shorter games and therefore the total number of running games decreased.
I can also tell, that since the slow-server-problem in 2012 from time to time (every few months) I manually checked the number of active players. And this was holding steady between 3000-3300 users (being active within 1 week) during the last 2 years. So there does not seem a decrease in active users, but just that the per-capita games is decreasing. The small increase in 2013/08 is probably explained by the new ladder-tournaments.
All that being said, I'm not sure, that the total number of running games is a good indicator for the "health" of the server.
If you take a look on the webserver-stats http://www.dragongoserver.net/stat/
you can even see a slight increase of usage over the last year. Though it's hard to set this in correlation as an increase in web-hits can have a variety of reasons (same user base doing more requests for example). So there's an increase in activity, but hard to tell what's the reasons for it.
It's probably interesting what criteria makes a "healthy" state: number of active users, number of games, usage of features, ??
It's a todo of replacing this stats with more meaningful charts as the current one can be misinterpreted perhaps, though so far I'm not sure what make some better stats. Any ideas?
Would be nice to see numbers from other servers to have a comparison and see if there are general trends for the up and downs or some migration between servers