A number of users are reporting significant screen flicker from the Nexus 7 tablet under low light conditions. The issue appears to surface when back-light is dimmed under 30%, a weak WiFi signal and the device is accessing the net.
I noticed this flicker myself last night on the device. The screen brightness was low and I was uploading data at the time. The flicker appeared to be worse when looking at an angle.
Although certainly not a deal-breaker for the Nexus 7, I do hope this is something Google will be able to provide a fix for.