I have now taken use of a new feature or 1.6.2, which allows to freeze time. So far, plugins have had this feature, but they would reset the time every minute, and cause lag. So the darklands has now been frozen to 23:00 – permanently, without the use of additional plugins. So no more sunrises, no more “safe time” from mobs! Enjoy :)
Also, I have made some conclusions from user reports, logfiles etc regarding the darklands. It appears that when someone wanders the darklands, all auto-generated storage minecarts in the underground mines are being added to the minecart mania database. I am not sure how much lag they cause, but they are listed in the database as “moving” and are in there until restart of the server. I filed a bug report with the plugin author, we will see if this gets fixed.