According to this report, SG-1 and Atlantis did indeed suffer low ratings for their season premiers on Friday 14 July:
LOSERS
SciFi’s “Stargate SG-1/Stargate: Atlantis” — This SciFi Network franchise took a laser hit to the gut on Friday night in the two shows’ latest season debuts. Ratings for the original “Stargate SG-1” (1.7 million) are down 15 percent from the season average earlier this year, while spinoff “Stargate: Atlantis” (1.9 million) dropped 10 percent.
Those viewer numbers would translate into Nielsen household ratings of 1.4 for SG-1 and 1.5 for Atlantis based on a conversion of 2.1 households = 2.6 viewers, which was the case in last season’s premiere.
Let’s cross our fingers that the ratings go up from here, or chances of renewal will be diminished.
Thanks to Java Dog of the Television Without Pity SG-1 forum for the original tip.