If you try to analyze your logs and notice that the Console Log is full of logs such as this one (happen every 30 seconds):
Jul 5 11:30:39 MYCOMPUTER hwmond: could not convert interface name
This type of log happens with Mac OS X server when there is a network port that is not recognized, such as the ones that are added by a video card (the RS422 ports). Even if that log has no incidence on the performance of your mac (unlike the DNS issue), this can be easily solved.
To solve this, just go in the Network Settings and remove all the ports that were added when you installed your video card.
Before you remove the port :
After you removed the port: